Partial implementation of CSHARP-433. Implemented OfType query operator. Still need to implement "is" operator and comparison of types using "==".

Author: rstam

Driver/Driver.csproj

@@ -183,6 +183,7 @@
     <Compile Include="Internal\MongoUpdateMessage.cs" />
     <Compile Include="Internal\ReplicaSetConnector.cs" />
     <Compile Include="Linq\Expressions\ExpressionFormatter.cs" />
+    <Compile Include="Linq\Expressions\ExpressionParameterFinder.cs" />
     <Compile Include="Linq\Expressions\ExpressionParameterReplacer.cs" />
     <Compile Include="Linq\LinqToMongo.cs" />
     <Compile Include="Linq\Translators\DeserializationProjector.cs" />

Driver/Linq/Expressions/ExpressionParameterFinder.cs

@@ -0,0 +1,82 @@
+/* Copyright 2010-2012 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;
+
+namespace MongoDB.Driver.Linq
+{
+    /// <summary>
+    /// A class that finds the first parameter in an expression.
+    /// </summary>
+    public class ExpressionParameterFinder : ExpressionVisitor
+    {
+        // private fields
+        private ParameterExpression _parameter;
+
+        // constructors
+        /// <summary>
+        /// Initializes a new instance of the ExpressionParameterFinder class.
+        /// </summary>
+        public ExpressionParameterFinder()
+        {
+        }
+
+        // public static methods
+        /// <summary>
+        /// Finds the first parameter in an expression.
+        /// </summary>
+        /// <param name="node">The expression containing the parameter that should be found.</param>
+        /// <returns>The first parameter found in the expression (or null if none was found).</returns>
+        public static ParameterExpression FindParameter(Expression node)
+        {
+            var finder = new ExpressionParameterFinder();
+            finder.Visit(node);
+            return finder._parameter;
+        }
+
+        // protected methods
+        /// <summary>
+        /// Visits an Expression.
+        /// </summary>
+        /// <param name="node">The Expression.</param>
+        /// <returns>The Expression (posibly modified).</returns>
+        protected override Expression Visit(Expression node)
+        {
+            if (_parameter != null)
+            {
+                return node; // exit faster if we've already found the parameter
+            }
+            return base.Visit(node);
+        }
+
+        /// <summary>
+        /// Remembers this parameter if it is the first parameter found.
+        /// </summary>
+        /// <param name="node">The ParameterExpression.</param>
+        /// <returns>The ParameterExpression.</returns>
+        protected override Expression VisitParameter(ParameterExpression node)
+        {
+            if (_parameter == null)
+            {
+                _parameter = node;
+            }
+            return node;
+        }
+    }
+}

Driver/Linq/Translators/SelectQuery.cs

@@ -37,6 +37,7 @@ public class SelectQuery : TranslatedQuery
     {
         // private fields
         private LambdaExpression _where;
+        private Type _ofType;
         private List<OrderByClause> _orderBy;
         private LambdaExpression _projection;
         private Expression _skip;
@@ -56,6 +57,14 @@ public SelectQuery(MongoCollection collection, Type documentType)
         }
 
         // public properties
+        /// <summary>
+        /// Gets the final result type if an OfType query operator was used (otherwise null).
+        /// </summary>
+        public Type OfType
+        {
+            get { return _ofType; }
+        }
+
         /// <summary>
         /// Gets a list of Expressions that defines the sort order (or null if not specified).
         /// </summary>
@@ -157,6 +166,21 @@ public override object Execute()
                 cursor.SetLimit(ToInt32(_take));
             }
 
+            if (_ofType != null)
+            {
+                if (_projection == null)
+                {
+                    var paramExpression = Expression.Parameter(DocumentType, "x");
+                    var convertExpression = Expression.Convert(paramExpression, _ofType);
+                    _projection = Expression.Lambda(convertExpression, paramExpression);
+                }
+                else
+                {
+                    // TODO: handle projection after OfType
+                    throw new NotSupportedException();
+                }
+            }
+
             IEnumerable enumerable;
             if (_projection == null)
             {
@@ -208,6 +232,7 @@ public void Translate(Expression expression)
             }
 
             var message = string.Format("Don't know how to translate expression: {0}.", ExpressionFormatter.ToString(expression));
+            throw new NotSupportedException(message);
         }
 
         // private methods
@@ -1239,10 +1264,39 @@ private void CombinePredicateWithWhereClause(MethodCallExpression methodCallExpr
                     return;
                 }
 
+                if (_where.Parameters.Count != 1)
+                {
+                    throw new MongoInternalException("Where lambda expression should have one parameter.");
+                }
                 var whereBody = _where.Body;
-                var predicateBody = ExpressionParameterReplacer.ReplaceParameter(predicate.Body, predicate.Parameters[0], _where.Parameters[0]);
+                var whereParameter = _where.Parameters[0];
+
+                if (predicate.Parameters.Count != 1)
+                {
+                    throw new MongoInternalException("Predicate lambda expression should have one parameter.");
+                }
+                var predicateBody = predicate.Body;
+                var predicateParameter = predicate.Parameters[0];
+
+                // when using OfType the parameter types might not match (but they do have to be compatible)
+                ParameterExpression parameter;
+                if (predicateParameter.Type.IsAssignableFrom(whereParameter.Type))
+                {
+                    predicateBody = ExpressionParameterReplacer.ReplaceParameter(predicateBody, predicateParameter, whereParameter);
+                    parameter = whereParameter;
+                }
+                else if (whereParameter.Type.IsAssignableFrom(predicateParameter.Type))
+                {
+                    whereBody = ExpressionParameterReplacer.ReplaceParameter(whereBody, whereParameter, predicateParameter);
+                    parameter = predicateParameter;
+                }
+                else
+                {
+                    throw new NotSupportedException("Can't combine existing where clause with new predicate because parameter types are incompatible.");
+                }
+
                 var combinedBody = Expression.AndAlso(whereBody, predicateBody);
-                _where = Expression.Lambda(combinedBody, _where.Parameters.ToArray());
+                _where = Expression.Lambda(combinedBody, parameter);
             }
         }
 
@@ -1278,7 +1332,9 @@ private object ExecuteDistinct(IMongoQuery query)
 
         private BsonSerializationInfo GetSerializationInfo(Expression expression)
         {
-            var documentSerializer = BsonSerializer.LookupSerializer(DocumentType);
+            // when using OfType the documentType used by the parameter might be a subclass of the DocumentType from the collection
+            var parameterExpression = ExpressionParameterFinder.FindParameter(expression);
+            var documentSerializer = BsonSerializer.LookupSerializer(parameterExpression.Type);
             return GetSerializationInfo(documentSerializer, expression);
         }
 
@@ -1755,6 +1811,9 @@ private void TranslateMethodCall(MethodCallExpression methodCallExpression)
                 case "Min":
                     TranslateMaxMin(methodCallExpression);
                     break;
+                case "OfType":
+                    TranslateOfType(methodCallExpression);
+                    break;
                 case "OrderBy":
                 case "OrderByDescending":
                     TranslateOrderBy(methodCallExpression);
@@ -1781,6 +1840,63 @@ private void TranslateMethodCall(MethodCallExpression methodCallExpression)
             }
         }
 
+        private void TranslateOfType(MethodCallExpression methodCallExpression)
+        {
+            var method = methodCallExpression.Method;
+            if (method.DeclaringType != typeof(Queryable))
+            {
+                var message = string.Format("OfType method of class {0} is not supported.", BsonUtils.GetFriendlyTypeName(method.DeclaringType));
+                throw new NotSupportedException(message);
+            }
+            if (!method.IsStatic)
+            {
+                throw new NotSupportedException("Expected OfType to be a static method.");
+            }
+            if (!method.IsGenericMethod)
+            {
+                throw new NotSupportedException("Expected OfType to be a generic method.");
+            }
+            var actualType = method.GetGenericArguments()[0];
+
+            var args = methodCallExpression.Arguments.ToArray();
+            if (args.Length != 1)
+            {
+                throw new NotSupportedException("Expected OfType method to have a single argument.");
+            }
+            var sourceExpression = args[0];
+            if (!sourceExpression.Type.IsGenericType)
+            {
+                throw new NotSupportedException("Expected source argument to OfType to be a generic type.");
+            }
+            var nominalType = sourceExpression.Type.GetGenericArguments()[0];
+
+            if (nominalType == actualType)
+            {
+                return; // nothing to do
+            }
+
+            if (_projection != null)
+            {
+                throw new NotSupportedException("OfType after a projection is not supported.");
+            }
+
+            var discriminatorConvention = BsonDefaultSerializer.LookupDiscriminatorConvention(nominalType);
+            var discriminator = discriminatorConvention.GetDiscriminator(nominalType, actualType);
+            if (discriminator.IsBsonArray)
+            {
+                discriminator = discriminator.AsBsonArray[discriminator.AsBsonArray.Count - 1];
+            }
+
+            var injectMethodInfo = typeof(LinqToMongo).GetMethod("Inject");
+            var query = Query.EQ("_t", discriminator);
+            var body = Expression.Call(injectMethodInfo, Expression.Constant(query));
+            var parameter = Expression.Parameter(nominalType, "x");
+            var predicate = Expression.Lambda(body, parameter);
+            CombinePredicateWithWhereClause(methodCallExpression, predicate);
+
+            _ofType = actualType;
+        }
+
         private void TranslateOrderBy(MethodCallExpression methodCallExpression)
         {
             if (methodCallExpression.Arguments.Count != 2)

DriverUnitTests/DriverUnitTests.csproj

@@ -162,6 +162,8 @@
     <Compile Include="Jira\CSharp93Tests.cs" />
     <Compile Include="Jira\CSharp98Tests.cs" />
     <Compile Include="Jira\CSharp100Tests.cs" />
+    <Compile Include="Linq\SelectOfTypeHierarchicalTests.cs" />
+    <Compile Include="Linq\SelectOfTypeTests.cs" />
     <Compile Include="Linq\SelectQueryTests.cs" />
     <Compile Include="Linq\MongoQueryableTests.cs" />
     <Compile Include="Linq\MongoQueryProviderTests.cs" />

DriverUnitTests/GridFS/MongoGridFSStreamTests.cs

@@ -282,7 +282,9 @@ public void TestUpdateMD5()
             {
                 var bytes = new byte[] { 1, 2, 3, 4 };
                 stream.Write(bytes, 0, 4);
+#pragma warning disable 618 // about obsolete BsonBinarySubType.OldBinary
                 stream.UpdateMD5 = false;
+#pragma warning restore
             }
 
             fileInfo = _gridFS.FindOne("test");