Entity Framework get specific column from a string

Question

I have a Web API project that uses Entity Framework. I have an action api/account that given an ID returns that account.

There is an additional parameter that can be provided which is what fields to be returned e.g. api/account?field=name

I'm trying to work out the best way of translating from this string input to Entity Framework. I know I can use .Select() to only get certain columns but that takes in a Func and the only way I can think of getting from the string to a Func is by using Reflection. This seems like it will be a peformance hit if I have to do Reflection for every property passed in, is there a better way of doing this?

Thanks

If you really need to return a dynamic subset of the columns in your API, I would still select them all from the DB and use some code (probably just if/else statements) to map the columns you want to the object you are returning from the API. — Ryan
– Ryan, Commented Jul 7, 2016 at 14:28
I just saw your older question. I'd advise you not to build dynamic queries to populate drop downs. Just create a specific endpoint for each type of data you need. AccountID/Name only vs all account details. — Ryan
– Ryan, Commented Jul 7, 2016 at 14:34
@Ryan that's what I was thinking, creating a separate endpoint for these. I was just thinking about going the dynamic route for future proofing if I need to get specific fields later. — ADringer
– ADringer, Commented Jul 7, 2016 at 14:40
Are you sure you need Reflection? It seems that you can do this with Expressions (see Expression.MakeMemberAccess and the like) — Alexey Merson
– Alexey Merson, Commented Jul 8, 2016 at 11:24
For situations like this, you can build a sql and execute it through the context.Database. using (var context = new myContext()) { result = context.Database.SqlQuery<T>(sql).ToList(); } — ssanga
– ssanga, Commented Jul 8, 2016 at 14:53

Mohammad Akbari · Accepted Answer · 2016-07-11 05:15:30Z

1

You can use this library System.Linq.Dynamic from Nuget, and this query

var selectStatement = string.Format("new ({0},{1})", field1, field2);
var result = db.Users.Select(selectStatement).ToListAsync().Result;

answered Jul 11, 2016 at 5:15

Mohammad Akbari

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