ADO.NET Entity: LINQ to Entity with Relationship

Relationship and getting data from Entity Framework using Northwind database

Simple Query

using (NorthwindEntities ctx = new NorthwindEntities())

{

var query = from o in ctx.Orders

select o.OrderID;

foreach (var k in query)

{

Console.WriteLine(k);

}

}

Now if you want to filter this with the parent information,

var query = from o in ctx.Orders

where o.Customers.City == "London"

select o.OrderID;

This actually goes one level up and then filters the data.

Include Child Information

var query = from c in ctx.Customers

where c.City == "London"

select c;

foreach (var k in query)

{

Console.WriteLine(k.ContactName);

}

Now if you want to get the “Orders” table, there are two ways to do it,

Immediate Loading

var query = from c in ctx.Customers.Include("Orders")

where c.City == "London"

select c;

foreach (var k in query)

{

Console.WriteLine(k.Orders.Count);

}

On-Demand Loading

var query = from c in ctx.Customers

where c.City == "London"

select c;

foreach (var k in query)

{

//if not loaded then load it

if (!k.Orders.IsLoaded)

k.Orders.Load();

Console.WriteLine(k.Orders.Count);

}

Namoskar!!!