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
&& 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;
}
}