How can I call local method in Linq to Entities query?

问题

I have the following code:

public void SalesCount(string customerId)
{
  ..
  ..
  return ...;
}

var resultQuery = dataContext.Customers
.Where (c => c.Name == "Alugili")
.Where (c => SalesCount(c.CustomerId) < 100);

When I execute resultQuery I get a translation to SQL exception.

I need to call SalesCount in the Where can I do that is there any workaround for this problem!

回答1:

Simply you can't. You can't execute C# code on the SQL server directly, you can use only Expressions and some special recognized functions...

Unless you transform your query (at least partially) in a LINQ-to-Objects...

var resultQuery = dataContext.Customers
    .Where (c => c.Name == "Alugili")
    .AsEnumerable()
    .Where (c => SalesCount(c.CustomerId) < 100);

Be aware that the last Where will be executed on the client side, so many useless rows will be fetched from the DB.

回答2:

Try

var resultQuery = dataContext.Customers
.Where (c => c.Name == "Alugili")
.ToArray()
.Where (c => SalesCount(c.CustomerId) < 100);

But then the second Where is not run as SQL but locally - all customers with the name "Alugili" are pulled from the DB...

Otherwise you have to write out your method directly in the where method as lambda expression.

回答3:

Add && between two where condition..It will work

回答4:

yes, you can.

but you should change return type for your function:

public **int** SalesCount(string customerId)
{
  ..
  ..
  return 500;
}


var resultQuery = dataContext.Customers.AsEnumerable()
                 .Where (c => c.Name == "Alugili" && SalesCount(c.CustomerId) < 100);

来源：https://stackoverflow.com/questions/18714821/how-can-i-call-local-method-in-linq-to-entities-query

标签

.net

linq

entity-framework