DataLoadOptions in LINQ allows immediate loading and filtering of related data. DataLoadOptions allows to load related objects, so this removes the need for firing a subquery every time you ask for related object(s).

Consider the below case:

If you do code like this:

var distlist = (from d in edb.Distributors select d).ToList();
foreach(Distributor d in distlist)
{
  var clientlist = d.Customers;
  foreach( Customer c in clientlist)
  {
       //do the code 
  }
}

Each time, the inner for loop fires a query on the database to get the customer related to the distributor which in turn decreases performance. But if you know in advance that you will need to use the related list when you are loading the main list, i.e., you need to load data of related entities, make use of DataLoadOptions.

The modified code is something like:

DataLoadOptions dlo = new DataLoadOptions();
dlo.LoadWith<Distributorgt;(d => d.Customers);
dataContext.LoadOptions = dlo;

Note

• Be careful when you use DataLoadOptions because it may decrease performance if you are not going to use related objects. Use only in situations when you want to load related objects early and you are going to consume it all.
• You an only attach DataLoadOptions once with the instance of a DataContext.

The above DataLoadOptions runs perfectly when you use regular LINQ queries. But it does not work with compiled queries. When you run this code and the query hits a second time, it produces an exception.

DataLoadOptions in Complied Queries

First, to get more information about complied queries, take a look at this post: Increase LINQ query performance by compiling it. Now when you attach DataLoadOptions to a complied query as we did above, it gives you an exception at run-time.

Compiled queries across DataContexts with different LoadOptions not supported

To avoid the exception, you need to create a static DataLoadOptions variable because as the compiled LINQ queries are static, they will not consume DataLoadOptions which is not static.

So for that, I have created the below code where the GetDataLoadOpt() static function returns the DataLoadOptions object and I store it into a static variable dlo and than attach dlo1 with the compiled version of the query.

public static DataLoadOptions dlo1 = GetDataLoadOpt();

public static Func<DataLoadTestDataContext, string, IQueryable<Product>>
    ProductByCategory =
    CompiledQuery.Compile((DataLoadTestDataContext db, string category) =>
    from p in db.Products where p.Category == category select p);

public static DataLoadOptions GetDataLoadOpt()
{
    DataLoadOptions dlo = new DataLoadOptions();
    dlo.LoadWith<Product>(p => p.ProductWithCategory);
    return dlo;
}

public static void testfunction()
{
    DataLoadTestDataContext context = new DataLoadTestDataContext();
    context.LoadOptions = dlo1;
    var productlist = ProductByCategory(context, "mobile");

    foreach (Product p in productlist)
    {
        Console.WriteLine(p.ProductWithCategory);
    }
}

If you want to get the above exception, try code after removing static from the function v and variable dlo1 and then assign it to the compiled version of the query, and you will get the run-time exception.