How can I extract a list of Tuple from a specific table with Entity Framework / LINQ?
.net c# entity-framework linq list
Question
I need to extract a list of couple 'ID'/'Name' from a large table in C# .NET with Entity Framework.
I try this request :
List<Tuple<int, string>> list = (from res in db.Resource
select new Tuple<int, string>(res.Resource_ID, res.Name)).ToList();
But unfortunately I've got this error :
Only parameterless constructors and initializers are supported in LINQ to Entities.
I don't undestand how can I extract this list of tuple with this framework and I feel a bit lost with this error. Can you help me to understand and resolve my problem ?
Best regards,
Alex
Accepted Answer
You can do it with a middle-step by selecting an anonymous type:
db.Resource.Select(x => new { x.Resource_ID, x.Name }).AsEnumerable().Select(x => Tuple.Create(x.Resource_ID, x.Name)).ToList();
Creating a tuple is not a supported operation in Linq To Entities, so you have to select an anonymous type, which would be an equivalent to:
SELECT [Resource].[Resource_ID], [Resource].[Name]
then move to LINQ to Objects by AsEnumerable and get your tuple.
Popular Answer
You can create a list from db.Resource and use LINQ to Collections to erase this limitation:
var list = db.Resource.ToList().Select(res => Tuple.Create(res.Resource_ID, res.Name));
The Tuple class does have some constructors (up to 8 items), but the Create() helper method makes the creation more straightforward.
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