Do Multiple Linq To Entity Queries In Entity Framework Using One DBContext Connect Only Once To The Database

Question

I am trying to return two result sets from an SQL Server database using Entity Framework 6. I would like to try this by running 2 Linq to Entity queries using a single DBContext. My question is by using a single DBContext is whether my request is only being hit by a database connection once. I think it is but I am not sure.

class RequestRefLists
{
  public List<Employee> EmployeeList {get;set;}
  public List<Dept> DeptList {get;set;}
}

    public RequestRefLists GetRequestRefLists()
   {
    RequestRefLists ReqRefLists = new RequestRefLists();

    using(var context= new BusinessDBContext())
    { 
      var queryResult1 = from e in context.Employees
      select e;
      ReqRefLists.EmployeeList = (List<Employee>)queryResult1.ToList();

      var queryResult2 = from d in context.Departments
      select d;
      ReqRefLists.DeptList = (List<Dept>)queryResult2.ToList();
    }
    return ReqRefLists;
   }

A simple glance at the executed SQL statements could have answered your question. — Gert Arnold
– Gert Arnold, Commented Dec 24, 2015 at 8:50

Vadim Martynov · Accepted Answer · 2015-12-24 06:50:06Z

8

You can use Entity Framework Extended Library.

There is a feature named Future queries

class RequestRefLists
{
    public List<Employee> EmployeeList {get;set;}
    public List<Dept> DeptList {get;set;}
}

public RequestRefLists GetRequestRefLists()
{
    RequestRefLists ReqRefLists = new RequestRefLists();

    using(var context= new BusinessDBContext)
    { 
        var queryResult1 = from e in context.Employees
        select e;
        ReqRefLists.EmployeeList = queryResult1.Future();

        var queryResult2 = from d in context.Departments
        select d;
        ReqRefLists.DeptList = queryResult2.Future();        
    }
    return ReqRefLists;
}

Your queries will execute lazy on first enumeration of any collection.

ExecuteFutureQueries builds a batch query from all the stored IFutureQuery objects. Finally, all the IFutureQuery objects are updated with the results from the query.

edited Dec 24, 2015 at 6:50

answered Dec 24, 2015 at 6:43

Vadim Martynov

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4 Comments

Sundar Singh Over a year ago

Question is do entity framework hit database only once when using same dbcontext object for multiple linq.

Vadim Martynov Over a year ago

@SundarSingh and Future() does exactly this.

Robertcode Over a year ago

If I understand it correctly it appears you can stack your queries within a single dbcontext each with the word .Future at the assignment point. In my case that is where I want to load a particular list in a custom class. After all queries have been defined I just enumerate one of them and all the assignments to my class instance are supposed to be performed in a single database connection. I'll test this. I am trying to load all the lookup lists from tables for a UI. I wonder if the extensions are officially part of Entity Framework. Thanks Vadim.

Vadim Martynov Over a year ago

There is no built mechanism to combine multiple queries in one batch. It is the reason of existence of EF Extended Library. Why do not you want to include 1 nuget package?

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