Create a Dynamic Entity Framework Where Query

Question

At runtime I have a dynamic list of "Parent" ids i need to query against one of my entity tables, using LINQ how would I generate the query at run time? Currently am (VERY SLOWLY) looping over my list of ID's and performing a separate query to the database using the Where method. Is there an API that will allow me to build a single WHERE statement that in essence is appending "&& value = something" as I would have if I was writing the SQL myself?

Currently what i do looks like this

            foreach(var parent in parents)
        {
            col.AddRange(context.LocalAuthorities.Where(c => c.Parent.ID == parent.ID).ToList());
        }

Please, add more details. What is your current query?

Maciej Los
– Maciej Los

2015-04-13 18:59:32 +00:00
Commented Apr 13, 2015 at 18:59 — Maciej Los
– Maciej Los, Commented Apr 13, 2015 at 18:59
will add an example.

Jarmez De La Rocha
– Jarmez De La Rocha

2015-04-13 19:18:55 +00:00
Commented Apr 13, 2015 at 19:18 — Jarmez De La Rocha
– Jarmez De La Rocha, Commented Apr 13, 2015 at 19:18

JimiLoe · Accepted Answer · 2015-04-13 21:55:25Z

1

If your goal is to replace multiple iterative queries by one query, you can use this approach:

var allParentIds = parents.Select(p=>p.ID).ToList();
var result = context.LocalAuthorities.Where(c=> allParentIds.Contains(c.Parent.ID));

col.AddRange(result);

answered Apr 13, 2015 at 21:55

JimiLoe

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2 Comments

Jarmez De La Rocha Over a year ago

I didn't think entity framework could translate a contains method call. I know this works with linq to objects, I will try this and get back to you. :)

Jarmez De La Rocha Over a year ago

Perfect and simple, i guess i should have checked before assuming it would not works. Much appreciated!

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