LINQ to Entities Example Queries

 

LINQ to Entities Example Queries Here are the examples I used during my LINQ to Entities presentation. They show how to use the EntityClient, ObjectQuery, and LINQ to Entities queries. All examples are built using a 1:1 mapping to the Adventure Works database that had been slightly modified. The Object Services with Lazy Loading Example shows some how to debug these queries. Entity Client Example // Entity Client & Entity SQL using (EntityConnection conn = new EntityConnection("Name=AdventureWorksEntities")) { conn.Open(); EntityCommand cmd = conn.CreateCommand(); cmd.CommandText = "SELECT VALUE c FROM AdventureWorksEntities.Customer AS c WHERE c.State = @state"; cmd.Parameters.AddWithValue("state", "UT"); DbDataReader rdr = cmd.ExecuteReader( CommandBehavior.SequentialAccess); while (rdr.Read()) { Console.WriteLine(string.Format("Company Name: {0}/tCompany City: {1}", rdr["CompanyName"], rdr["City"])); } } Object Services Query Example // Object Services & Entity SQL using (AdventureWorksEntities data = new AdventureWorksEntities()) { ObjectQuery custs = data.CreateQuery( "SELECT VALUE c FROM Customer AS c WHERE c.Address.City = @city", new ObjectParameter("city", "Salt Lake City")); foreach (Customer cust in custs) { Console.WriteLine("Company: " + cust.CompanyName); } } Object Services Query with Eager Loading Example // Eager Loading with Object Services using (AdventureWorksEntities data = new AdventureWorksEntities()) { ObjectQuery custs = data.CreateQuery( "SELECT VALUE c FROM Customer AS c WHERE c.State = @state", new ObjectParameter("state", "UT")).Include("SalesOrderHeader"); foreach (Customer cust in custs) { SalesOrderHeader sales = cust.SalesOrderHeader.FirstOrDefault(); string str = (sales == null) ? "none" : sales.OrderDate .ToShortDateString(); Console.WriteLine( string.Format("Company: {0}/tOrder: {1}", cust.CompanyName, str)); } } Object Services Query with Lazy Loading Example // Lazy Loading with Object Services using (AdventureWorksEntities data = new AdventureWorksEntities()) { ObjectQuery custs = data.CreateQuery( "SELECT VALUE c FROM Customer AS c WHERE c.State = @state", new ObjectParameter("state", "UT")); Console.WriteLine("DEBUG: " + custs.ToTraceString()); foreach (Customer cust in custs) { if (!cust.SalesOrderHeader.IsLoaded) cust.SalesOrderHeader.Load(); SalesOrderHeader sales = cust.SalesOrderHeader.FirstOrDefault(); string str = (sales == null) ? "none" : sales.OrderDate .ToShortDateString(); Console.WriteLine( string.Format("Company: {0}/tOrder: {1}", cust.CompanyName, str)); } } LINQ to Entities Query Example // LINQ to ENTIES (Lazy Loading) using (AdventureWorksEntities data = new AdventureWorksEntities()) { var custquery = from d in data.Customer where d.State == "UT" select d; foreach (Customer cust in custquery) { if ( !cust.SalesOrderHeader.IsLoaded ) cust.SalesOrderHeader.Load(); SalesOrderHeader sales = cust.SalesOrderHeader .FirstOrDefault(); string str = (sales == null) ? "none" : sales.OrderDate .ToShortDateString(); Console.WriteLine( string.Format("Company: {0}/tOrder: {1}", cust.CompanyName, str)); } } The presentation slides are available here.