How to convert DbSet in Entity framework to ObjectQuery

Question

I am using CodeFirst approach and struck with an issue where I need to convert DbSet to ObjectQuery. This is what I did for conversion.

ObjectContext objectContext = ((IObjectContextAdapter)db).ObjectContext;
ObjectSet<Request> objectSet = objectContext.CreateObjectSet<Request>();

where db is the context inheriting from DbContext and Request is class.

So, when I try to call the method that expects ObjectQuery as ObjectQueryMethod(objectSet), it throws the following error.

"Type of conditional expression cannot be determined because there is no implicit conversion between 'System.Data.Entity.DbSet<>' and 'System.Data.Objects.ObjectQuery<>'"

Any help is greatly appreciated!

Provide more details - what is `ObjectQueryMethod`? Your current approach is correct. You cannot convert `DbSet` to `ObjectQuery`. You must create `ObjectSet` and use it instead of `DbSet`. — Ladislav Mrnka, Jun 29 '12 at 08:23
@Kittoes: I am trying to implement Advanced searching in JQGrid and ObjectQuery seems to be the right one to parse the parameters (filters) sent back to the server. — inspiringmyself, Jun 29 '12 at 13:23
@LadislavMrnka: It's just a method that expects ObjectQuery as a parameter (named as such) :) — inspiringmyself, Jun 29 '12 at 13:27
Thanks everyone for your time. I figured out what I was missing, I need to pass the DbSet("Requests") to ObjectSet as ObjectSet objectSet = objectContext.CreateObjectSet("Requests"); — inspiringmyself, Jun 29 '12 at 13:32

score 23 · Accepted Answer · edited Sep 16 '15 at 13:09

23

I found the answer. Of course, it is possible to convert DbSet in Entity framework to ObjectQuery using the below lines of code.

ObjectContext objectContext = ((IObjectContextAdapter)db).ObjectContext;  
ObjectSet<Request> objectSet = objectContext.CreateObjectSet<Request>("Requests");

where,

db - Context class inherting from DbContext.
Requests - DbSet<Request> defined in Context class.
objectSet - Can now be passed as ObjectQuery.

edited Sep 16 '15 at 13:09

Duncan Smart

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answered Jun 29 '12 at 13:29

inspiringmyself

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AFAIK you can leave the string out as parameter, which makes it less error-pron: `objectContext.CreateObjectSet();` – Yahoo Serious Apr 12 '13 at 13:33

score 2 · Answer 2 · edited Aug 17 '15 at 10:06

Thanks for the correct answer 'inspiringmyself'; this is just to elaborate on your answer. I managed to do this with a generic type, so just to share it:

private List<T> GetByCustomCriteria<T>(string criteria) where T: class
{
  var objectContext = ((IObjectContextAdapter)_myModelEntities).ObjectContext;
  //note: _myModelEntities is a DbContext in EF6.
  var objectSet = objectContext.CreateObjectSet<T>();
  return new List<T>(objectSet.Where(criteria));
 }

And I thought the above post could do with an example of what criteria to send so here's an example:

 //sample criteria for int field:
 var myClientById = GetByCustomCriteria<Client>("it.Id == 1");`

//sample criteria for string field, note the single quotes
var myClientByName = GetByCustomCriteria<Client>("it.Surname == 'Simpson'");

How to convert DbSet in Entity framework to ObjectQuery

2 Answers2

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