/// <summary>
/// This will never return null
/// </summary>
public Func <IQueryable <TSource>, IEnumerable <TDest> > GetProjection()
{
return(source => source
.Select(_sourceTypeToInterimTypeConversion.GetTypeConverterFuncExpression())
.AsEnumerable()
.Select(_interimTypeToDestTypeConversion.Convert));
}
private Expression GetEnumerableConversionExpression(Expression propertyValueParam)
{
if (propertyValueParam == null)
{
throw new ArgumentNullException("propertyValueParam");
}
if (!typeof(IEnumerable <TPropertyOnSourceElement>).IsAssignableFrom(propertyValueParam.Type))
{
throw new ArgumentException("propertyValueParam.Type must match be assignable to IEnumerable<TPropertyOnSourceElement>");
}
// This translation (using LINQ's Select method) from IEnumerable<TPropertyOnSourceElement> to IEnumerable<TPropertyAsRetrievedElement> is supported
// by Entity Framework and may be used for the translation of IQueryable results
var selectMethod = typeof(Enumerable).GetMethods()
.Select(m => new
{
Method = m,
GenericArguments = m.GetGenericArguments(),
Parameters = m.GetParameters()
})
.Where(m =>
(m.Method.Name == "Select") &&
(m.GenericArguments.Length == 2) &&
(m.Parameters.Length == 2) &&
(m.Parameters[0].ParameterType == typeof(IEnumerable <>).MakeGenericType(m.GenericArguments[0])) &&
(m.Parameters[1].ParameterType == typeof(Func <,>).MakeGenericType(m.GenericArguments[0], m.GenericArguments[1]))
)
.Select(m => m.Method.MakeGenericMethod(typeof(TPropertyOnSourceElement), typeof(TPropertyAsRetrievedElement)))
.Single();
return(Expression.Call(
selectMethod,
propertyValueParam,
_typeConverter.GetTypeConverterFuncExpression()
));
}