How to write entity framework query and Linq query on c#?

Question

Hi, I have this table. I want to write this query in my controller.

select sum(Amount) from tbl_Amounts where fk_Roleid=2

which shows result of 800 in sql. I don't know how to write it in both EF and Linq. If someone could kindly show me the way to write in both ways would be really helpfull.

Answer 1

This should basically be the Linq syntax for your request.

Linq is some "internal framework" of .NET / C#, and you use Entity framework.

There is no real meaning in separating the two, in my opinion.

This is the "Linq to SQL" syntax I would use on the "DataContext" that you cretate with EF :

DataContext
    .tbl_Amounts
    .Where(a => a.fk_Roleid = 2)
    .Sum(a => a.Amount);

If you have a collection of record called Amounts, this would be the "linq to objects" version :

Amounts
    .Where(a => a.fk_Roleid = 2)
    .Sum(a => a.Amount);

As you can see, there is no real difference ! (excepted that, under the hood, the first one on an EF Data Context will be converted to a SQL db request)

But it could actually depends on your Entity Framework version (not all linq features are correctly translated to SQL)

Answer 2

There are 3 different ways to execute SQL query in Entity Framework (EF), depending on the version you're using:

1) Using LINQ to Entities (all versions)

using (var db = new DataContext())
{
    int amount = (from am in db.tbl_Amounts where am.fk_Roleid == 2 select am.amount).Sum();
}

2) Using Database.SqlQuery<T>() (up to EF 6)

using (var db = new DataContext())
{
    string query = "select sum(Amount) from tbl_Amounts where fk_Roleid=2";
    int amount = db.Database.SqlQuery<int>(query).Single(); // or First()
}

3) Using FromSql() (EF Core)

using (var db = new DataContext())
{
    string query = "select sum(Amount) from tbl_Amounts where fk_Roleid=2";
    int amount = db.tbl_Amounts.FromSql(query).Single(); // or First()
}

Note that if you're using EF Core, Database.SqlQuery<T> doesn't exist and you should use Execute raw SQL query in EF Core .