in tools/AutoMapper/QueryableExtensions/Impl/SourceInjectedQueryProvider.cs [72:217]
public TResult Execute<TResult>(Expression expression)
{
try
{
var resultType = typeof(TResult);
Inspector.StartQueryExecuteInterceptor(resultType, expression);
var sourceExpression = ConvertDestinationExpressionToSourceExpression(expression);
var destResultType = typeof(TResult);
var sourceResultType = CreateSourceResultType(destResultType);
object destResult = null;
// case #1: query is a projection from complex Source to complex Destination
// example: users.UseAsDataSource().For<UserDto>().Where(x => x.Age > 20).ToList()
if (IsProjection<TDestination>(resultType))
{
// in case of a projection, we need an IQueryable
var sourceResult = _dataSource.Provider.CreateQuery(sourceExpression);
Inspector.SourceResult(sourceExpression, sourceResult);
destResult = new ProjectionExpression((IQueryable<TSource>)sourceResult, _mapper.ConfigurationProvider.ExpressionBuilder).To<TDestination>(_parameters, _membersToExpand);
}
// case #2: query is arbitrary ("manual") projection
// exaple: users.UseAsDataSource().For<UserDto>().Select(user => user.Age).ToList()
// in case an arbitrary select-statement is enumerated, we do not need to map the expression at all
// and cann safely return it
else if (IsProjection(resultType, sourceExpression))
{
var sourceResult = _dataSource.Provider.CreateQuery(sourceExpression);
var enumerator = sourceResult.GetEnumerator();
var elementType = ElementTypeHelper.GetElementType(typeof(TResult));
var constructorInfo = typeof(List<>).MakeGenericType(elementType).GetDeclaredConstructor(new Type[0]);
if (constructorInfo != null)
{
var listInstance = (IList)constructorInfo.Invoke(null);
while (enumerator.MoveNext())
{
listInstance.Add(enumerator.Current);
}
destResult = listInstance;
}
}
// case #2: projection to simple type
// example: users.UseAsDataSource().For<UserDto>().FirstOrDefault(user => user.Age > 20)
else
{
/*
in case of an element result (so instead of IQueryable<TResult>, just TResult)
we still want to support parameters.
This is e.g. the case, when the developer writes "UseAsDataSource().For<TResult>().FirstOrDefault(x => ...)
To still be able to support parameters, we need to create a query from it.
That said, we need to replace the "element" operator "FirstOrDefault" with a "Where" operator, then apply our "Select"
to map from TSource to TResult and finally re-apply the "element" operator ("FirstOrDefault" in our case) so only
one element is returned by our "Execute<TResult>" method. Otherwise we'd get an InvalidCastException
* So first we visit the sourceExpression and replace "element operators" with "where"
* then we create our mapping expression from TSource to TDestination (select) and apply it
* finally, we search for the element expression overload of our replaced "element operator" that has no expression as parameter
this expression is not needed anymore as it has already been applied to the "Where" operation and can be safely omitted
* when we're done creating our new expression, we call the underlying provider to execute it
*/
// as we need to replace the innermost element of the expression,
// we need to traverse it first in order to find the node to replace or potential caveats
// e.g. .UseAsDataSource().For<Dto>().Select(e => e.Name).First()
// in the above case we cannot map anymore as the "select" operator overrides our mapping.
var searcher = new ReplaceableMethodNodeFinder<TSource>();
searcher.Visit(sourceExpression);
// provide the replacer with our found MethodNode or <null>
var replacer = new MethodNodeReplacer<TSource>(searcher.MethodNode);
// default back to simple mapping of object instance for backwards compatibility (e.g. mapping non-nullable to nullable fields)
sourceExpression = replacer.Visit(sourceExpression);
if (replacer.FoundElementOperator)
{
/* in case of primitive element operators (e.g. Any(), Sum()...)
we need to map the originating types (e.g. Entity to Dto) in this query
as the final value will be projected automatically
== example 1 ==
UseAsDataSource().For<Dto>().Any(entity => entity.Name == "thename")
..in that case sourceResultType and destResultType would both be "Boolean" which is not mappable for AutoMapper
== example 2 ==
UseAsDataSource().For<Dto>().FirstOrDefault(entity => entity.Name == "thename")
..in this case the sourceResultType would be Entity and the destResultType Dto, so we can map the query directly
*/
if (sourceResultType == destResultType)// && destResultType.IsPrimitive)
{
sourceResultType = typeof(TSource);
destResultType = typeof(TDestination);
}
var membersToExpand = _membersToExpand.SelectMany(m => m).Distinct().ToArray();
var lambdas = _mapper.ConfigurationProvider.ExpressionBuilder.GetMapExpression(sourceResultType, destResultType,
_parameters, membersToExpand);
// add projection via "select" operator
var expr = lambdas.Aggregate(sourceExpression, (source, lambda) => Select(source, lambda));
// in case an element operator without predicate expression was found (and thus not replaced)
var replacementMethod = replacer.ElementOperator;
// in case an element operator with predicate expression was replaced
if (replacer.ReplacedMethod != null)
{
// find replacement method that has no more predicates
replacementMethod = typeof(Queryable).GetAllMethods()
.Single(m => m.Name == replacer.ReplacedMethod.Name
#if NET45 || NET40
&& m.GetParameters().All(p => typeof(Queryable).IsAssignableFrom(p.Member.ReflectedType))
#endif
&& m.GetParameters().Length == replacer.ReplacedMethod.GetParameters().Length - 1);
}
// reintroduce element operator that was replaced with a "where" operator to make it queryable
expr = Expression.Call(null,
replacementMethod.MakeGenericMethod(destResultType), expr);
destResult = _dataSource.Provider.Execute(expr);
}
// If there was no element operator that needed to be replaced by "where", just map the result
else
{
var sourceResult = _dataSource.Provider.Execute(sourceExpression);
Inspector.SourceResult(sourceExpression, sourceResult);
destResult = _mapper.Map(sourceResult, sourceResultType, destResultType);
}
}
Inspector.DestResult(destResult);
// implicitly convert types in case of valuetypes which cannot be casted explicitly
if (typeof(TResult).IsValueType() && destResult?.GetType() != typeof(TResult))
return (TResult)Convert.ChangeType(destResult, typeof(TResult));
// if it is not a valuetype, we can safely cast it
return (TResult)destResult;
}
catch (Exception x)
{
_exceptionHandler(x);
throw;
}
}