Implemented CSHARP-351. When the BsonClassMapSerializer encounters an error deserializing a field or property the name of the field or property as well as the name of the class they are in are included in the error message to assist the user in troubleshooting the problem.

Bson/Exceptions/TruncationException.cs

@@ -30,7 +30,7 @@ namespace MongoDB.Bson {
         /// Initializes a new instance of the TruncationException class.
         /// </summary>
         public TruncationException()
-            : base() {
+            : this("Truncation resulted in data loss.") {
         }
 
         /// <summary>

Bson/Serialization/BsonClassMapSerializer.cs

@@ -112,6 +112,11 @@ namespace MongoDB.Bson.Serialization {
                 }
                 var obj = classMap.CreateInstance();
 
+                if (bsonReader.CurrentBsonType != BsonType.Document) {
+                    var message = string.Format("Expected a nested document representing the serialized form of a {0} value, but found a value of type {1} instead.", actualType.FullName, bsonReader.CurrentBsonType);
+                    throw new FileFormatException(message);
+                }
+
                 bsonReader.ReadStartDocument();
                 var missingElementMemberMaps = new HashSet<BsonMemberMap>(classMap.MemberMaps); // make a copy!
                 var discriminatorConvention = BsonDefaultSerializer.LookupDiscriminatorConvention(nominalType);
@@ -294,17 +299,28 @@ namespace MongoDB.Bson.Serialization {
             object obj,
             BsonMemberMap memberMap
         ) {
-            var nominalType = memberMap.MemberType;
-            Type actualType;
-            if (bsonReader.CurrentBsonType == BsonType.Null) {
-                actualType = nominalType;
-            } else {
-                var discriminatorConvention = BsonDefaultSerializer.LookupDiscriminatorConvention(nominalType);
-                actualType = discriminatorConvention.GetActualType(bsonReader, nominalType); // returns nominalType if no discriminator found
+            try {
+                var nominalType = memberMap.MemberType;
+                Type actualType;
+                if (bsonReader.CurrentBsonType == BsonType.Null) {
+                    actualType = nominalType;
+                } else {
+                    var discriminatorConvention = BsonDefaultSerializer.LookupDiscriminatorConvention(nominalType);
+                    actualType = discriminatorConvention.GetActualType(bsonReader, nominalType); // returns nominalType if no discriminator found
+                }
+                var serializer = memberMap.GetSerializer(actualType);
+                var value = serializer.Deserialize(bsonReader, nominalType, actualType, memberMap.SerializationOptions);
+                memberMap.Setter(obj, value);
+            } catch (Exception ex) {
+                var message = string.Format(
+                    "An error occurred while deserializing the {0} {1} of class {2}: {3}", // terminating period provided by nested message
+                    memberMap.MemberName,
+                    (memberMap.MemberInfo.MemberType == MemberTypes.Field) ? "field" : "property",
+                    obj.GetType().FullName,
+                    ex.Message
+                );
+                throw new FileFormatException(message, ex);
             }
-            var serializer = memberMap.GetSerializer(actualType);
-            var value = serializer.Deserialize(bsonReader, nominalType, actualType, memberMap.SerializationOptions);
-            memberMap.Setter(obj, value);
         }
 
         private void SerializeExtraElements(

BsonUnitTests/BsonUnitTests.csproj

@@ -137,6 +137,7 @@
     <Compile Include="Jira\CSharp338Tests.cs" />
     <Compile Include="Jira\CSharp310Tests.cs" />
     <Compile Include="Jira\CSharp350Tests.cs" />
+    <Compile Include="Jira\CSharp351Tests.cs" />
     <Compile Include="Jira\CSharp70Tests.cs" />
     <Compile Include="Jira\CSharp71Tests.cs" />
     <Compile Include="Jira\CSharp74Tests.cs" />

BsonUnitTests/DefaultSerializer/Serializers/BsonValueSerializerTests.cs

@@ -435,7 +435,15 @@ namespace MongoDB.BsonUnitTests.Serialization {
             Assert.AreEqual(expected, json);
 
             var bson = obj.ToBson();
-            Assert.Throws<NotSupportedException>(() => BsonSerializer.Deserialize<TestClass>(bson));
+            try {
+                BsonSerializer.Deserialize<TestClass>(bson);
+                Assert.Fail("Expected an exception to be thrown.");
+            } catch (Exception ex) {
+                var expectedMessage = "An error occurred while deserializing the V property of class MongoDB.BsonUnitTests.Serialization.BsonDocumentWrapperSerializerTests+TestClass: Specified method is not supported.";
+                Assert.IsInstanceOf<FileFormatException>(ex);
+                Assert.IsInstanceOf<NotSupportedException>(ex.InnerException);
+                Assert.AreEqual(expectedMessage, ex.Message);
+            }
         }
 
         [Test]
@@ -446,7 +454,15 @@ namespace MongoDB.BsonUnitTests.Serialization {
             Assert.AreEqual(expected, json);
 
             var bson = obj.ToBson();
-            Assert.Throws<NotSupportedException>(() => BsonSerializer.Deserialize<TestClass>(bson));
+            try {
+                BsonSerializer.Deserialize<TestClass>(bson);
+                Assert.Fail("Expected an exception to be thrown.");
+            } catch (Exception ex) {
+                var expectedMessage = "An error occurred while deserializing the V property of class MongoDB.BsonUnitTests.Serialization.BsonDocumentWrapperSerializerTests+TestClass: Specified method is not supported.";
+                Assert.IsInstanceOf<FileFormatException>(ex);
+                Assert.IsInstanceOf<NotSupportedException>(ex.InnerException);
+                Assert.AreEqual(expectedMessage, ex.Message);
+            }
         }
 
         [Test]
@@ -464,7 +480,15 @@ namespace MongoDB.BsonUnitTests.Serialization {
             Assert.AreEqual(expected, json);
 
             var bson = obj.ToBson();
-            Assert.Throws<NotSupportedException>(() => BsonSerializer.Deserialize<TestClass>(bson));
+            try {
+                BsonSerializer.Deserialize<TestClass>(bson);
+                Assert.Fail("Expected an exception to be thrown.");
+            } catch (Exception ex) {
+                var expectedMessage = "An error occurred while deserializing the V property of class MongoDB.BsonUnitTests.Serialization.BsonDocumentWrapperSerializerTests+TestClass: Specified method is not supported.";
+                Assert.IsInstanceOf<FileFormatException>(ex);
+                Assert.IsInstanceOf<NotSupportedException>(ex.InnerException);
+                Assert.AreEqual(expectedMessage, ex.Message);
+            }
         }
     }
 

BsonUnitTests/Jira/CSharp351Tests.cs

@@ -0,0 +1,55 @@
+/* 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.IO;
+using System.Linq;
+using System.Runtime.Serialization;
+using System.Text;
+using System.Xml;
+using NUnit.Framework;
+
+using MongoDB.Bson;
+using MongoDB.Bson.IO;
+using MongoDB.Bson.Serialization;
+
+namespace MongoDB.BsonUnitTests.Jira {
+    [TestFixture]
+    public class CSharp351Tests {
+        private class C {
+            public int _id { get; set; }
+            public N N { get; set; }
+        }
+
+        private class N {
+            public int X { get; set; }
+        }
+
+        [Test]
+        public void TestErrorMessage() {
+            var json = "{ _id : 1, N : 'should be a document, not a string' }";
+            try {
+                var c = BsonSerializer.Deserialize<C>(json);
+                Assert.Fail("Expected an exception to be thrown.");
+            } catch (Exception ex) {
+                var expected = "An error occurred while deserializing the N property of class MongoDB.BsonUnitTests.Jira.CSharp351Tests+C: Expected a nested document representing the serialized form of a MongoDB.BsonUnitTests.Jira.CSharp351Tests+N value, but found a value of type String instead.";
+                Assert.IsInstanceOf<FileFormatException>(ex);
+                Assert.IsInstanceOf<FileFormatException>(ex.InnerException);
+                Assert.AreEqual(expected, ex.Message);
+            }
+        }
+    }
+}

DriverOnlineTests/Jira/CSharp112Tests.cs

@@ -106,7 +106,15 @@ namespace MongoDB.DriverOnlineTests.Jira.CSharp112 {
 
             for (int i = 0; i < values.Length; i++) {
                 var query = Query.EQ("_id", i + 1);
-                Assert.Throws<TruncationException>(() => collection.FindOneAs<D>(query));
+                try {
+                    collection.FindOneAs<D>(query);
+                    Assert.Fail("Expected an exception to be thrown.");
+                } catch (Exception ex) {
+                    var expectedMessage = "An error occurred while deserializing the N field of class MongoDB.DriverOnlineTests.Jira.CSharp112.CSharp112Tests+D: Truncation resulted in data loss.";
+                    Assert.IsInstanceOf<FileFormatException>(ex);
+                    Assert.IsInstanceOf<TruncationException>(ex.InnerException);
+                    Assert.AreEqual(expectedMessage, ex.Message);
+                }
             }
         }
 
@@ -160,7 +168,15 @@ namespace MongoDB.DriverOnlineTests.Jira.CSharp112 {
 
             for (int i = 0; i < values.Length; i++) {
                 var query = Query.EQ("_id", i + 1);
-                Assert.Throws<OverflowException>(() => collection.FindOneAs<I>(query));
+                try {
+                    collection.FindOneAs<I>(query);
+                    Assert.Fail("Expected an exception to be thrown.");
+                } catch (Exception ex) {
+                    var expectedMessage = "An error occurred while deserializing the N field of class MongoDB.DriverOnlineTests.Jira.CSharp112.CSharp112Tests+I: Arithmetic operation resulted in an overflow.";
+                    Assert.IsInstanceOf<FileFormatException>(ex);
+                    Assert.IsInstanceOf<OverflowException>(ex.InnerException);
+                    Assert.AreEqual(expectedMessage, ex.Message);
+                }
             }
 
             // test with values that cause truncation
@@ -179,7 +195,15 @@ namespace MongoDB.DriverOnlineTests.Jira.CSharp112 {
 
             for (int i = 0; i < values.Length; i++) {
                 var query = Query.EQ("_id", i + 1);
-                Assert.Throws<TruncationException>(() => collection.FindOneAs<I>(query));
+                try {
+                    collection.FindOneAs<I>(query);
+                    Assert.Fail("Expected an exception to be thrown.");
+                } catch (Exception ex) {
+                    var expectedMessage = "An error occurred while deserializing the N field of class MongoDB.DriverOnlineTests.Jira.CSharp112.CSharp112Tests+I: Truncation resulted in data loss.";
+                    Assert.IsInstanceOf<FileFormatException>(ex);
+                    Assert.IsInstanceOf<TruncationException>(ex.InnerException);
+                    Assert.AreEqual(expectedMessage, ex.Message);
+                }
             }
         }
 
@@ -234,7 +258,15 @@ namespace MongoDB.DriverOnlineTests.Jira.CSharp112 {
 
             for (int i = 0; i < values.Length; i++) {
                 var query = Query.EQ("_id", i + 1);
-                Assert.Throws<OverflowException>(() => collection.FindOneAs<L>(query));
+                try {
+                    collection.FindOneAs<L>(query);
+                    Assert.Fail("Expected an exception to be thrown.");
+                } catch (Exception ex) {
+                    var expectedMessage = "An error occurred while deserializing the N field of class MongoDB.DriverOnlineTests.Jira.CSharp112.CSharp112Tests+L: Arithmetic operation resulted in an overflow.";
+                    Assert.IsInstanceOf<FileFormatException>(ex);
+                    Assert.IsInstanceOf<OverflowException>(ex.InnerException);
+                    Assert.AreEqual(expectedMessage, ex.Message);
+                }
             }
 
             // test with values that cause data truncation
@@ -253,7 +285,15 @@ namespace MongoDB.DriverOnlineTests.Jira.CSharp112 {
 
             for (int i = 0; i < values.Length; i++) {
                 var query = Query.EQ("_id", i + 1);
-                Assert.Throws<TruncationException>(() => collection.FindOneAs<L>(query));
+                try {
+                    collection.FindOneAs<L>(query);
+                    Assert.Fail("Expected an exception to be thrown.");
+                } catch (Exception ex) {
+                    var expectedMessage = "An error occurred while deserializing the N field of class MongoDB.DriverOnlineTests.Jira.CSharp112.CSharp112Tests+L: Truncation resulted in data loss.";
+                    Assert.IsInstanceOf<FileFormatException>(ex);
+                    Assert.IsInstanceOf<TruncationException>(ex.InnerException);
+                    Assert.AreEqual(expectedMessage, ex.Message);
+                }
             }
         }
     }

DriverOnlineTests/Jira/CSharp218Tests.cs

@@ -60,7 +60,15 @@ namespace MongoDB.DriverOnlineTests.Jira.CSharp218 {
             collection.RemoveAll();
             var c = new C { Id = ObjectId.GenerateNewId(), P = new P { X = 1, Y = 2 } };
             collection.Insert(c);
-            Assert.Throws<BsonSerializationException>(() => collection.FindOneAs<C>());
+            try {
+                collection.FindOneAs<C>();
+                Assert.Fail("Expected an exception to be thrown.");
+            } catch (Exception ex) {
+                var expectedMessage = "An error occurred while deserializing the P field of class MongoDB.DriverOnlineTests.Jira.CSharp218.CSharp218Tests+C: Value class MongoDB.DriverOnlineTests.Jira.CSharp218.CSharp218Tests+P cannot be deserialized.";
+                Assert.IsInstanceOf<FileFormatException>(ex);
+                Assert.IsInstanceOf<BsonSerializationException>(ex.InnerException);
+                Assert.AreEqual(expectedMessage, ex.Message);
+            }
         }
 
         [Test]