Initial framework of LINQ implementation. Please note that this doesn't really do anything yet because the MongoLinqTranslator class is stubbed out.

Bson/Serialization/BsonClassMap.cs

@@ -1031,17 +1031,19 @@ namespace MongoDB.Bson.Serialization {
 
         private Func<object> GetCreator() {
             if (creator == null) {
-                Expression expression;
+                Expression body;
                 var bindingFlags = BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance;
                 var defaultConstructor = classType.GetConstructor(bindingFlags, null, new Type[0], null);
                 if (defaultConstructor != null) {
-                    expression = Expression.New(defaultConstructor);
+                    // lambdaExpression = () => (object) new TClass()
+                    body = Expression.New(defaultConstructor);
                 } else {
-                    var getUnitializedObjectInfo = typeof(FormatterServices).GetMethod("GetUninitializedObject", BindingFlags.Public | BindingFlags.Static);
-                    expression = Expression.Call(getUnitializedObjectInfo, Expression.Constant(classType));
+                    // lambdaExpression = () => FormatterServices.GetUninitializedObject(classType)
+                    var getUnitializedObjectMethodInfo = typeof(FormatterServices).GetMethod("GetUninitializedObject", BindingFlags.Public | BindingFlags.Static);
+                    body = Expression.Call(getUnitializedObjectMethodInfo, Expression.Constant(classType));
                 }
-                var lambda = Expression.Lambda<Func<object>>(expression);
-                creator = lambda.Compile();
+                var lambdaExpression = Expression.Lambda<Func<object>>(body);
+                creator = lambdaExpression.Compile();
             }
             return creator;
         }
@@ -1056,14 +1058,15 @@ namespace MongoDB.Bson.Serialization {
                 shouldSerializeMethodInfo.IsPublic &&
                 shouldSerializeMethodInfo.ReturnType == typeof(bool)
             ) {
-                // we need to construct a lambda wich does the following
-                // (obj) => obj.ShouldSerializeXyz()
-                var parameter = Expression.Parameter(typeof(object), "obj");
-                var body = Expression.Call(
-                    Expression.Convert(parameter, classType),
-                    shouldSerializeMethodInfo
+                // lambdaExpression = (obj) => ((TClass) obj).ShouldSerializeXyz()
+                var objParameter = Expression.Parameter(typeof(object), "obj");
+                var lambdaExpression = Expression.Lambda<Func<object, bool>>(
+                    Expression.Call(
+                        Expression.Convert(objParameter, classType),
+                        shouldSerializeMethodInfo
+                    ),
+                    objParameter
                 );
-                var lambdaExpression = Expression.Lambda<Func<object, bool>>(body, parameter);
                 return lambdaExpression.Compile();
             } else {
                 return null;

Bson/Serialization/BsonMemberMap.cs

@@ -420,19 +420,20 @@ namespace MongoDB.Bson.Serialization {
                 }
             }
 
-            var instance = Expression.Parameter(typeof(object), "obj");
-            var lambda = Expression.Lambda<Func<object, object>>(
+            // lambdaExpression = (obj) => (object) ((TClass) obj).Member
+            var objParameter = Expression.Parameter(typeof(object), "obj");
+            var lambdaExpression = Expression.Lambda<Func<object, object>>(
                 Expression.Convert(
                     Expression.MakeMemberAccess(
-                        Expression.Convert(instance, memberInfo.DeclaringType),
+                        Expression.Convert(objParameter, memberInfo.DeclaringType),
                         memberInfo
                     ),
                     typeof(object)
                 ),
-                instance
+                objParameter
             );
 
-            return lambda.Compile();
+            return lambdaExpression.Compile();
         }
 
         private Action<object, object> GetPropertySetter() {
@@ -443,19 +444,20 @@ namespace MongoDB.Bson.Serialization {
                 throw new BsonSerializationException(message);
             }
 
-            var instance = Expression.Parameter(typeof(object), "obj");
-            var argument = Expression.Parameter(typeof(object), "a");
-            var lambda = Expression.Lambda<Action<object, object>>(
+            // lambdaExpression = (obj, value) => ((TClass) obj).SetMethod((TMember) value)
+            var objParameter = Expression.Parameter(typeof(object), "obj");
+            var valueParameter = Expression.Parameter(typeof(object), "value");
+            var lambdaExpression = Expression.Lambda<Action<object, object>>(
                 Expression.Call(
-                    Expression.Convert(instance, memberInfo.DeclaringType),
+                    Expression.Convert(objParameter, memberInfo.DeclaringType),
                     setMethodInfo,
-                    Expression.Convert(argument, memberType)
+                    Expression.Convert(valueParameter, memberType)
                 ),
-                instance,
-                argument
+                objParameter,
+                valueParameter
             );
 
-            return lambda.Compile();
+            return lambdaExpression.Compile();
         }
         #endregion
     }

Driver/Driver.csproj

@@ -179,6 +179,13 @@
     <Compile Include="Internal\MongoReplyMessage.cs" />
     <Compile Include="Internal\MongoUpdateMessage.cs" />
     <Compile Include="Internal\ReplicaSetConnector.cs" />
+    <Compile Include="Linq\MongoLinqFindQuery.cs" />
+    <Compile Include="Linq\MongoLinqExtensionMethods.cs" />
+    <Compile Include="Linq\MongoQueryable.cs" />
+    <Compile Include="Linq\MongoQueryProvider.cs" />
+    <Compile Include="Linq\MongoLinqTranslator.cs" />
+    <Compile Include="Linq\MongoLinqQuery.cs" />
+    <Compile Include="Linq\TypeSystem.cs" />
     <Compile Include="MongoUtils.cs" />
     <Compile Include="MongoDefaults.cs" />
     <Compile Include="GridFS\MongoGridFS.cs" />

Driver/Linq/MongoLinqExtensionMethods.cs

@@ -0,0 +1,42 @@
+/* Copyright 2010-2011 10gen Inc.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Text;
+using System.Threading;
+
+namespace MongoDB.Driver.Linq {
+    /// <summary>
+    /// Static class that contains the Mongo Linq extension methods.
+    /// </summary>
+    public static class MongoLinqExtensionMethods {
+        /// <summary>
+        /// Returns an instance of IQueryable{{T}} for a MongoCollection.
+        /// </summary>
+        /// <typeparam name="T">The type of the returned documents.</typeparam>
+        /// <param name="collection">The name of the collection.</param>
+        /// <returns>An instance of IQueryable{{T}} for a MongoCollection.</returns>
+        public static IQueryable<T> AsQueryable<T>(
+            this MongoCollection collection
+        ) {
+            var provider = new MongoQueryProvider(collection);
+            return new MongoQueryable<T>(provider);
+        }
+    }
+}

Driver/Linq/MongoLinqFindQuery.cs

@@ -0,0 +1,59 @@
+/* Copyright 2010-2011 10gen Inc.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Text;
+using System.Threading;
+
+namespace MongoDB.Driver.Linq {
+    /// <summary>
+    /// Represents a LINQ query that has been translated to an equivalent MongoDB Find query.
+    /// </summary>
+    public class MongoLinqFindQuery : MongoLinqQuery {
+        #region private fields
+        private IMongoQuery query;
+        #endregion
+
+        #region constructor
+        /// <summary>
+        /// Initializes a new instance of the MongoLinqFindQuery class.
+        /// </summary>
+        /// <param name="collection">The collection being queried.</param>
+        /// <param name="query">The query.</param>
+        public MongoLinqFindQuery(
+            MongoCollection collection,
+            IMongoQuery query
+        )
+            : base(collection) {
+                this.query = query;
+        }
+        #endregion
+
+        #region public methods
+        /// <summary>
+        /// Executes the translated Find query.
+        /// </summary>
+        /// <returns>The result of executing the translated Find query.</returns>
+        public override IEnumerator<T> GetEnumerator<T>() {
+            var cursor = collection.FindAs<T>(query);
+            // TODO: modify the cursor with things like sort order, skip and limit
+            return cursor.GetEnumerator();
+        }
+        #endregion
+    }
+}

Driver/Linq/MongoLinqQuery.cs

@@ -0,0 +1,66 @@
+/* Copyright 2010-2011 10gen Inc.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Text;
+using System.Threading;
+
+namespace MongoDB.Driver.Linq {
+    /// <summary>
+    /// Represents a LINQ query that has been translated to a MongoDB query.
+    /// </summary>
+    public abstract class MongoLinqQuery {
+        #region protected fields
+        /// <summary>
+        /// The collection being queried.
+        /// </summary>
+        protected MongoCollection collection;
+        #endregion
+
+        #region constructors
+        /// <summary>
+        /// Initializes a new instance of the MongoLinqQuery class.
+        /// </summary>
+        /// <param name="collection">The collection being queried.</param>
+        protected MongoLinqQuery(
+            MongoCollection collection
+        ) {
+            this.collection = collection;
+        }
+        #endregion
+
+        #region public methods
+        /// <summary>
+        /// Executes a query that returns a single result (overridden by subclasses).
+        /// </summary>
+        /// <returns>The result of executing the query.</returns>
+        public virtual object Execute() {
+            throw new NotSupportedException();
+        }
+
+        /// <summary>
+        /// Gets an enumerator for the results of a query that returns multiple results (overridden by subclasses).
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        /// <returns></returns>
+        public virtual IEnumerator<T> GetEnumerator<T>() {
+            throw new NotSupportedException();
+        }
+        #endregion
+    }
+}

Driver/Linq/MongoLinqTranslator.cs

@@ -0,0 +1,45 @@
+/* Copyright 2010-2011 10gen Inc.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Text;
+using System.Threading;
+
+namespace MongoDB.Driver.Linq {
+    /// <summary>
+    /// A translator from LINQ expression queries to Mongo queries.
+    /// </summary>
+    public static class MongoLinqTranslator {
+        #region public static methods
+        /// <summary>
+        /// A translator from LINQ queries to MongoDB queries.
+        /// </summary>
+        /// <param name="collection">The collection being queried.</param>
+        /// <param name="expression">The LINQ query.</param>
+        /// <returns>An instance of MongoLinqQuery.</returns>
+        public static MongoLinqQuery Translate(
+            MongoCollection collection,
+            Expression expression
+        ) {
+            // total hack just to test the initial LINQ framework
+            var query = MongoDB.Driver.Builders.Query.EQ("X", 1);
+            return new MongoLinqFindQuery(collection, query);
+        }
+        #endregion
+    }
+}

Driver/Linq/MongoQueryProvider.cs

@@ -0,0 +1,233 @@
+/* Copyright 2010-2011 10gen Inc.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Text;
+using System.Threading;
+using System.Reflection;
+
+namespace MongoDB.Driver.Linq {
+    /// <summary>
+    /// An implementation of IQueryProvider for querying a MongoDB collection.
+    /// </summary>
+    public class MongoQueryProvider : IQueryProvider {
+        #region private static fields
+        private static Dictionary<Type, Func<MongoQueryProvider, Expression, IQueryable>> createQueryDelegates = new Dictionary<Type, Func<MongoQueryProvider, Expression, IQueryable>>();
+        private static MethodInfo createQueryGenericMethodDefinition;
+        private static Dictionary<Type, Func<MongoQueryProvider, Expression, object>> executeDelegates = new Dictionary<Type, Func<MongoQueryProvider, Expression, object>>();
+        private static MethodInfo executeGenericMethodDefinition;
+        private static object staticLock = new object();
+        #endregion
+
+        #region private fields
+        private MongoCollection collection;
+        #endregion
+
+        #region static constructor
+        static MongoQueryProvider() {
+            foreach (var methodInfo in typeof(MongoQueryProvider).GetMethods(BindingFlags.Public | BindingFlags.Instance | BindingFlags.DeclaredOnly)) {
+                if (methodInfo.Name == "CreateQuery" && methodInfo.IsGenericMethodDefinition) {
+                    createQueryGenericMethodDefinition = methodInfo;
+                }
+                if (methodInfo.Name == "Execute" && methodInfo.IsGenericMethodDefinition) {
+                    executeGenericMethodDefinition = methodInfo;
+                }
+            }
+        }
+        #endregion
+
+        #region constructors
+        /// <summary>
+        /// Initializes a new instance of the MongoQueryProvider class.
+        /// </summary>
+        public MongoQueryProvider(
+            MongoCollection collection
+        ) {
+            if (collection == null) {
+                throw new ArgumentNullException("collection");
+            }
+            this.collection = collection;
+        }
+        #endregion
+
+        #region private static methods
+        private static Func<MongoQueryProvider, Expression, IQueryable> GetCreateQueryDelegate(
+            Type type
+        ) {
+            lock (staticLock) {
+                Func<MongoQueryProvider, Expression, IQueryable> createQueryDelegate;
+                if (!createQueryDelegates.TryGetValue(type, out createQueryDelegate)) {
+                    var createQueryMethodInfo = createQueryGenericMethodDefinition.MakeGenericMethod(type);
+
+                    // lambdaExpression = (provider, expression) => (IQueryable) provider.CreateQuery<T>(expression)
+                    var providerParameter = Expression.Parameter(typeof(MongoQueryProvider), "provider");
+                    var expressionParameter = Expression.Parameter(typeof(Expression), "expression");
+                    var lambdaExpression = Expression.Lambda<Func<MongoQueryProvider, Expression, IQueryable>>(
+                        Expression.Convert(
+                            Expression.Call(providerParameter, createQueryMethodInfo, expressionParameter),
+                            typeof(IQueryable)
+                        ),
+                        providerParameter,
+                        expressionParameter
+                    );
+                    createQueryDelegate = lambdaExpression.Compile();
+                    createQueryDelegates.Add(type, createQueryDelegate);
+                }
+                return createQueryDelegate;
+            }
+        }
+
+        private static Func<MongoQueryProvider, Expression, object> GetExecuteDelegate(
+            Type type
+        ) {
+            lock (staticLock) {
+                Func<MongoQueryProvider, Expression, object> executeDelegate;
+                if (!executeDelegates.TryGetValue(type, out executeDelegate)) {
+                    var executeMethodInfo = executeGenericMethodDefinition.MakeGenericMethod(type);
+
+                    // lambdaExpression = (provider, expression) => (object) provider.Execute<T>(expression)
+                    var providerParameter = Expression.Parameter(typeof(MongoQueryProvider), "provider");
+                    var expressionParameter = Expression.Parameter(typeof(Expression), "expression");
+                    var lambdaExpression = Expression.Lambda<Func<MongoQueryProvider, Expression, object>>(
+                        Expression.Convert(
+                            Expression.Call(providerParameter, executeMethodInfo, expressionParameter),
+                            typeof(object)
+                        ),
+                        providerParameter,
+                        expressionParameter
+                    );
+                    executeDelegate = lambdaExpression.Compile();
+                    executeDelegates.Add(type, executeDelegate);
+                }
+                return executeDelegate;
+            }
+        }
+        #endregion
+
+        #region public methods
+        /// <summary>
+        /// Creates a new instance of MongoQueryable{{T}} for this provider.
+        /// </summary>
+        /// <typeparam name="T">The type of the returned elements.</typeparam>
+        /// <param name="expression">The query expression.</param>
+        /// <returns>A new instance of MongoQueryable{{T}}.</returns>
+        public IQueryable<T> CreateQuery<T>(
+            Expression expression
+        ) {
+            if (expression == null) {
+                throw new ArgumentNullException("expression");
+            }
+            if (!typeof(IQueryable<T>).IsAssignableFrom(expression.Type)) {
+                throw new ArgumentOutOfRangeException("expression");
+            }
+            return new MongoQueryable<T>(this, expression);
+        }
+
+        /// <summary>
+        /// Creates a new instance MongoQueryable{{T}} for this provider. Calls the generic CreateQuery{{T}} 
+        /// to actually create the new MongoQueryable{{T}} instance.
+        /// </summary>
+        /// <param name="expression">The query expression.</param>
+        /// <returns>A new instance of MongoQueryable{{T}}.</returns>
+        public IQueryable CreateQuery(
+            Expression expression
+        ) {
+            if (expression == null) {
+                throw new ArgumentNullException("expression");
+            }
+            try {
+                var elementType = TypeSystem.GetElementType(expression.Type);
+                var createQueryDelegate = GetCreateQueryDelegate(elementType);
+                return createQueryDelegate(this, expression);
+            } catch (TargetInvocationException ex) {
+                throw ex.InnerException;
+            }
+        }
+
+        /// <summary>
+        /// Executes a query.
+        /// </summary>
+        /// <typeparam name="TResult">The type of the result.</typeparam>
+        /// <param name="expression">The query expression.</param>
+        /// <returns>The result of the query.</returns>
+        public TResult Execute<TResult>(
+            Expression expression
+        ) {
+            if (expression == null) {
+                throw new ArgumentNullException("expression");
+            }
+            if (!typeof(TResult).IsAssignableFrom(expression.Type)) {
+                throw new ArgumentException("Argument expression is not valid.");
+            }
+            var translatedQuery = MongoLinqTranslator.Translate(collection, expression);
+            return (TResult) translatedQuery.Execute();
+        }
+
+        /// <summary>
+        /// Executes a query. Calls the generic method Execute{{T}} to actually execute the query.
+        /// </summary>
+        /// <param name="expression">The query expression.</param>
+        /// <returns>The result of the query.</returns>
+        public object Execute(
+            Expression expression
+        ) {
+            if (expression == null) {
+                throw new ArgumentNullException("expression");
+            }
+            try {
+                var resultType = expression.Type;
+                var executeDelegate = GetExecuteDelegate(resultType);
+                return executeDelegate(this, expression);
+            } catch (TargetInvocationException ex) {
+                throw ex.InnerException;
+            }
+        }
+
+        /// <summary>
+        /// Gets an enumerator by executing the query.
+        /// </summary>
+        /// <typeparam name="T">Type element type.</typeparam>
+        /// <param name="expression">The LINQ expression.</param>
+        /// <returns>An enumerator for the results of the query.</returns>
+        public IEnumerator<T> GetEnumerator<T>(
+            Expression expression
+        ) {
+            if (expression == null) {
+                throw new ArgumentNullException("expression");
+            }
+            if (!typeof(IEnumerable<T>).IsAssignableFrom(expression.Type)) {
+                throw new ArgumentException("Argument expression is not valid.");
+            }
+            var translatedQuery = MongoLinqTranslator.Translate(collection, expression);
+            return translatedQuery.GetEnumerator<T>();
+        }
+
+        /// <summary>
+        /// Gets a string representation of the LINQ expression translated to a MongoDB query.
+        /// </summary>
+        /// <param name="expression">The LINQ expression.</param>
+        /// <returns>A string.</returns>
+        public string GetQueryText(
+            Expression expression
+        ) {
+            var translatedQuery = MongoLinqTranslator.Translate(collection, expression);
+            return translatedQuery.ToString();
+        }
+        #endregion
+    }
+}

Driver/Linq/MongoQueryable.cs

@@ -0,0 +1,107 @@
+/* Copyright 2010-2011 10gen Inc.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Text;
+using System.Threading;
+
+namespace MongoDB.Driver.Linq {
+    /// <summary>
+    /// An implementation of IQueryable{{T}} for querying a MongoDB collection.
+    /// </summary>
+    public class MongoQueryable<T> : IOrderedQueryable<T> {
+        #region private fields
+        private MongoQueryProvider provider;
+        private Expression expression;
+        #endregion
+
+        #region constructors
+        /// <summary>
+        /// Initializes a new instance of the MongoQueryable class.
+        /// </summary>
+        public MongoQueryable(
+            MongoQueryProvider provider
+        ) {
+            if (provider == null) {
+                throw new ArgumentNullException("provider");
+            }
+            this.provider = provider;
+            this.expression = Expression.Constant(this);
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the MongoQueryable class.
+        /// </summary>
+        public MongoQueryable(
+            MongoQueryProvider provider,
+            Expression expression
+        ) {
+            if (provider == null) {
+                throw new ArgumentNullException("provider");
+            }
+            if (expression == null) {
+                throw new ArgumentNullException("expression");
+            }
+            if (!typeof(IQueryable<T>).IsAssignableFrom(expression.Type)) {
+                throw new ArgumentOutOfRangeException("expression");
+            }
+            this.provider = provider;
+            this.expression = expression;
+        }
+        #endregion
+
+        #region public methods
+        /// <summary>
+        /// Gets an enumerator for the results of a MongoDB LINQ query.
+        /// </summary>
+        /// <returns></returns>
+        public IEnumerator<T> GetEnumerator() {
+            return provider.GetEnumerator<T>(expression);
+        }
+
+        /// <summary>
+        /// Gets a string representation of the MongoDB query obtained by translating the LINQ query.
+        /// </summary>
+        /// <returns></returns>
+        public override string ToString() {
+            return provider.GetQueryText(expression);
+        }
+        #endregion
+
+        #region explicit implementation of IEnumerable
+        IEnumerator IEnumerable.GetEnumerator() {
+            return GetEnumerator();
+        }
+        #endregion
+
+        #region explicit implementation of IQueryable
+        Type IQueryable.ElementType {
+            get { return typeof(T); }
+        }
+
+        Expression IQueryable.Expression {
+            get { return expression; }
+        }
+
+        IQueryProvider IQueryable.Provider {
+            get { return provider; }
+        }
+        #endregion
+    }
+}

Driver/Linq/TypeSystem.cs

@@ -0,0 +1,64 @@
+/* Copyright 2010-2011 10gen Inc.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading;
+
+namespace MongoDB.Driver.Linq {
+    // taken from http://msdn.microsoft.com/en-us/library/bb546158.aspx
+    internal static class TypeSystem {
+        internal static Type GetElementType(Type seqType) {
+            Type ienum = FindIEnumerable(seqType);
+            if (ienum == null) { return seqType; }
+            return ienum.GetGenericArguments()[0];
+        }
+
+        private static Type FindIEnumerable(Type seqType) {
+            if (seqType == null || seqType == typeof(string)) {
+                return null;
+            }
+
+            if (seqType.IsArray) {
+                return typeof(IEnumerable<>).MakeGenericType(seqType.GetElementType());
+            }
+
+            if (seqType.IsGenericType) {
+                foreach (Type arg in seqType.GetGenericArguments()) {
+                    Type ienum = typeof(IEnumerable<>).MakeGenericType(arg);
+                    if (ienum.IsAssignableFrom(seqType)) {
+                        return ienum;
+                    }
+                }
+            }
+
+            Type[] ifaces = seqType.GetInterfaces();
+            if (ifaces != null && ifaces.Length > 0) {
+                foreach (Type iface in ifaces) {
+                    Type ienum = FindIEnumerable(iface);
+                    if (ienum != null) { return ienum; }
+                }
+            }
+
+            if (seqType.BaseType != null && seqType.BaseType != typeof(object)) {
+                return FindIEnumerable(seqType.BaseType);
+            }
+
+            return null;
+        }
+    }
+}

DriverOnlineTests/DriverOnlineTests.csproj

@@ -119,6 +119,9 @@
     <Compile Include="Jira\CSharp93Tests.cs" />
     <Compile Include="Jira\CSharp98Tests.cs" />
     <Compile Include="Jira\CSharp100Tests.cs" />
+    <Compile Include="Linq\MongoLinqFindQueryTests.cs" />
+    <Compile Include="Linq\MongoQueryableTests.cs" />
+    <Compile Include="Linq\MongoQueryProviderTests.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="Samples\MagicDiscriminatorTests.cs" />
   </ItemGroup>

DriverOnlineTests/Linq/MongoLinqFindQueryTests.cs

@@ -0,0 +1,69 @@
+/* Copyright 2010-2011 10gen Inc.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using NUnit.Framework;
+
+using MongoDB.Bson;
+using MongoDB.Bson.Serialization.Attributes;
+using MongoDB.Driver;
+using MongoDB.Driver.Builders;
+using MongoDB.Driver.Linq;
+
+namespace MongoDB.DriverOnlineTests.Linq {
+    [TestFixture]
+    public class MongoLinqFindQueryTests {
+        private class C {
+            public ObjectId Id { get; set; }
+            public int X { get; set; }
+            public int Y { get; set; }
+        }
+
+        private MongoServer server;
+        private MongoDatabase database;
+        private MongoCollection<C> collection;
+
+        [TestFixtureSetUp]
+        public void Setup() {
+            server = MongoServer.Create("mongodb://localhost/?safe=true");
+            server.Connect();
+            database = server["onlinetests"];
+            collection = database.GetCollection<C>("linqtests");
+
+            collection.Drop();
+            collection.Insert(new C { X = 1, Y = 11 });
+            collection.Insert(new C { X = 2, Y = 12 });
+            collection.Insert(new C { X = 3, Y = 13 });
+            collection.Insert(new C { X = 4, Y = 14 });
+            collection.Insert(new C { X = 5, Y = 15 });
+        }
+
+        [Test]
+        public void TestQueryXEquals1() {
+            var query = from c in collection.AsQueryable<C>()
+                        where c.X == 1
+                        select c;
+            var count = 0;
+            foreach (var c in query) {
+                Assert.AreEqual(1, c.X);
+                count++;
+            }
+            Assert.AreEqual(1, count);
+        }
+   }
+}

DriverOnlineTests/Linq/MongoQueryProviderTests.cs

@@ -0,0 +1,75 @@
+/* Copyright 2010-2011 10gen Inc.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Text;
+using NUnit.Framework;
+
+using MongoDB.Bson;
+using MongoDB.Bson.Serialization.Attributes;
+using MongoDB.Driver;
+using MongoDB.Driver.Builders;
+using MongoDB.Driver.Linq;
+
+namespace MongoDB.DriverOnlineTests.Linq {
+    [TestFixture]
+    public class MongoQueryProviderTests {
+        private class C {
+            public ObjectId Id { get; set; }
+            public int X { get; set; }
+            public int Y { get; set; }
+        }
+
+        private MongoServer server;
+        private MongoDatabase database;
+        private MongoCollection collection;
+
+        [TestFixtureSetUp]
+        public void Setup() {
+            server = MongoServer.Create("mongodb://localhost/?safe=true");
+            server.Connect();
+            database = server["onlinetests"];
+            collection = database["linqtests"];
+        }
+
+        [Test]
+        public void TestConstructor() {
+            var provider = new MongoQueryProvider(collection);
+        }
+
+        [Test]
+        public void TestCreateQuery() {
+            var expression = collection.AsQueryable<C>().Expression;
+            var provider = new MongoQueryProvider(collection);
+            var query = provider.CreateQuery<C>(expression);
+            Assert.AreSame(typeof(C), query.ElementType);
+            Assert.AreSame(provider, query.Provider);
+            Assert.AreSame(expression, query.Expression);
+        }
+
+        [Test]
+        public void TestCreateQueryNonGeneric() {
+            var expression = collection.AsQueryable<C>().Expression;
+            var provider = new MongoQueryProvider(collection);
+            var query = provider.CreateQuery(expression);
+            Assert.AreSame(typeof(C), query.ElementType);
+            Assert.AreSame(provider, query.Provider);
+            Assert.AreSame(expression, query.Expression);
+        }
+    }
+}

DriverOnlineTests/Linq/MongoQueryableTests.cs

@@ -0,0 +1,67 @@
+/* Copyright 2010-2011 10gen Inc.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Text;
+using NUnit.Framework;
+
+using MongoDB.Bson;
+using MongoDB.Bson.Serialization.Attributes;
+using MongoDB.Driver;
+using MongoDB.Driver.Builders;
+using MongoDB.Driver.Linq;
+
+namespace MongoDB.DriverOnlineTests.Linq {
+    [TestFixture]
+    public class MongoQueryableTests {
+        private class C {
+            public ObjectId Id { get; set; }
+            public int X { get; set; }
+            public int Y { get; set; }
+        }
+
+        private MongoServer server;
+        private MongoDatabase database;
+        private MongoCollection collection;
+
+        [TestFixtureSetUp]
+        public void Setup() {
+            server = MongoServer.Create("mongodb://localhost/?safe=true");
+            server.Connect();
+            database = server["onlinetests"];
+            collection = database["linqtests"];
+        }
+
+        [Test]
+        public void TestConstructorWithOneArgument() {
+            var provider = new MongoQueryProvider(collection);
+            var iqueryable = (IQueryable) new MongoQueryable<C>(provider);
+            Assert.AreSame(typeof(C), iqueryable.ElementType);
+            Assert.AreSame(provider, iqueryable.Provider);
+        }
+
+        [Test]
+        public void TestConstructorWithTwoArguments() {
+            var queryable = collection.AsQueryable<C>();
+            var iqueryable = (IQueryable) new MongoQueryable<C>((MongoQueryProvider) queryable.Provider, queryable.Expression);
+            Assert.AreSame(typeof(C), iqueryable.ElementType);
+            Assert.AreSame(queryable.Provider, iqueryable.Provider);
+            Assert.AreSame(queryable.Expression, iqueryable.Expression);
+        }
+    }
+}