Question

Visual Studio 2008 | Silverlight 3 | SQL Server 2005 | Domain Services Class | Entity Data Model

I have a database table “Students” with columns FirstName, LastName, Semester, ProgramOfStudy, Column etc…….

The goal is to return a Total (number of students grouped by first letter of lastname), based on the first letter of the lastname of all students in a given Semester and Programofstudy.

I was unsuccessful writing the LINQ query and thought I would try to use a SQL View.

1. Created the view (17,000 rows grouped down to 5000 rows).
2. The Views consists of ‘LastNameStartsWith’, ‘Total’, ‘AcademicPeriod’, ‘ProgramCode’.
3. Added the View to the .edmx model
4. Wrote the following queries.

As Linq;

public IQueryable GetVw_studentAlphabetSet(int cycleID, string progCode)
     {
          var query = from s in db.vw_studentAlphabetSet
          where ((s.programCode == progCode) && (s.academicPeriod == cycleID))
          select s;
          return query; 
}

When ran as sql with parameters filled in MSSMS the view filters down to 25 rows reporting the count of occurrences. A-Z, with X not reported as there are no lastnames starting with X.

If a breakpoint is set on return query;, it correctly reports an entity count of 24, but each entity is identical. LastNamesStartsWith = ‘A’ and Total = 21.

So it seems like the filtering is working but with a bug. Each entity should be unique A-Z.

If I add to the .Where like so

where (s.programCode == progCode) && (s.academicPeriod == cycleID) && (s.LastNameStartsWith == "B");

A correct return is generated. B, 35, 200890, BSED-ELED-ED

When using the Linq return elements, I get one measly element to use. LastNameStartsWith = “A” and Total = 21. But again B – Z and there totals are not returned. In the Domain Services Class, it did report that the elements count was 24. Where did they all go. I should have gotten 23 more elements even if they were all reporting A and 21.

So is there something special one should know when working with views and Linq?

Here the designer for the Entity Model

[assembly: global::System.Data.Objects.DataClasses.EdmSchemaAttribute()]

// Original file name:
// Generation date: 2/21/2010 10:25:00 PM
namespace sproc.Web
{

    /// 
    /// There are no comments for GLADYS_2010Entities in the schema.
    /// 
    public partial class GLADYS_2010Entities : global::System.Data.Objects.ObjectContext
    {
        /// 
        /// Initializes a new GLADYS_2010Entities object using the connection string found in the 'GLADYS_2010Entities' section of the application configuration file.
        /// 
        public GLADYS_2010Entities() : 
                base("name=GLADYS_2010Entities", "GLADYS_2010Entities")
        {
            this.OnContextCreated();
        }
        /// 
        /// Initialize a new GLADYS_2010Entities object.
        /// 
        public GLADYS_2010Entities(string connectionString) : 
                base(connectionString, "GLADYS_2010Entities")
        {
            this.OnContextCreated();
        }
        /// 
        /// Initialize a new GLADYS_2010Entities object.
        /// 
        public GLADYS_2010Entities(global::System.Data.EntityClient.EntityConnection connection) : 
                base(connection, "GLADYS_2010Entities")
        {
            this.OnContextCreated();
        }
        partial void OnContextCreated();
        /// 
        /// There are no comments for vw_studentAlphabet in the schema.
        /// 
        public global::System.Data.Objects.ObjectQuery vw_studentAlphabet
        {
            get
            {
                if ((this._vw_studentAlphabet == null))
                {
                    this._vw_studentAlphabet = base.CreateQuery("[vw_studentAlphabet]");
                }
                return this._vw_studentAlphabet;
            }
        }
        private global::System.Data.Objects.ObjectQuery _vw_studentAlphabet;
        /// 
        /// There are no comments for vw_studentAlphabet in the schema.
        /// 
        public void AddTovw_studentAlphabet(vw_studentAlphabet vw_studentAlphabet)
        {
            base.AddObject("vw_studentAlphabet", vw_studentAlphabet);
        }
    }
    /// 
    /// There are no comments for GLADYS_2010Model.vw_studentAlphabet in the schema.
    /// 
    /// 
    /// academicPeriod
    /// programCode
    /// 
    [global::System.Data.Objects.DataClasses.EdmEntityTypeAttribute(NamespaceName="GLADYS_2010Model", Name="vw_studentAlphabet")]
    [global::System.Runtime.Serialization.DataContractAttribute(IsReference=true)]
    [global::System.Serializable()]
    public partial class vw_studentAlphabet : global::System.Data.Objects.DataClasses.EntityObject
    {
        /// 
        /// Create a new vw_studentAlphabet object.
        /// 
        /// Initial value of academicPeriod.
        /// Initial value of programCode.
        public static vw_studentAlphabet Createvw_studentAlphabet(int academicPeriod, string programCode)
        {
            vw_studentAlphabet vw_studentAlphabet = new vw_studentAlphabet();
            vw_studentAlphabet.academicPeriod = academicPeriod;
            vw_studentAlphabet.programCode = programCode;
            return vw_studentAlphabet;
        }
        /// 
        /// There are no comments for Property LastNameStartsWith in the schema.
        /// 
        [global::System.Data.Objects.DataClasses.EdmScalarPropertyAttribute()]
        [global::System.Runtime.Serialization.DataMemberAttribute()]
        public string LastNameStartsWith
        {
            get
            {
                return this._LastNameStartsWith;
            }
            set
            {
                this.OnLastNameStartsWithChanging(value);
                this.ReportPropertyChanging("LastNameStartsWith");
                this._LastNameStartsWith = global::System.Data.Objects.DataClasses.StructuralObject.SetValidValue(value, true);
                this.ReportPropertyChanged("LastNameStartsWith");
                this.OnLastNameStartsWithChanged();
            }
        }
        private string _LastNameStartsWith;
        partial void OnLastNameStartsWithChanging(string value);
        partial void OnLastNameStartsWithChanged();
        /// 
        /// There are no comments for Property Total in the schema.
        /// 
        [global::System.Data.Objects.DataClasses.EdmScalarPropertyAttribute()]
        [global::System.Runtime.Serialization.DataMemberAttribute()]
        public global::System.Nullable Total
        {
            get
            {
                return this._Total;
            }
            set
            {
                this.OnTotalChanging(value);
                this.ReportPropertyChanging("Total");
                this._Total = global::System.Data.Objects.DataClasses.StructuralObject.SetValidValue(value);
                this.ReportPropertyChanged("Total");
                this.OnTotalChanged();
            }
        }
        private global::System.Nullable _Total;
        partial void OnTotalChanging(global::System.Nullable value);
        partial void OnTotalChanged();
        /// 
        /// There are no comments for Property academicPeriod in the schema.
        /// 
        [global::System.Data.Objects.DataClasses.EdmScalarPropertyAttribute(EntityKeyProperty=true, IsNullable=false)]
        [global::System.Runtime.Serialization.DataMemberAttribute()]
        public int academicPeriod
        {
            get
            {
                return this._academicPeriod;
            }
            set
            {
                this.OnacademicPeriodChanging(value);
                this.ReportPropertyChanging("academicPeriod");
                this._academicPeriod = global::System.Data.Objects.DataClasses.StructuralObject.SetValidValue(value);
                this.ReportPropertyChanged("academicPeriod");
                this.OnacademicPeriodChanged();
            }
        }
        private int _academicPeriod;
        partial void OnacademicPeriodChanging(int value);
        partial void OnacademicPeriodChanged();
        /// 
        /// There are no comments for Property programCode in the schema.
        /// 
        [global::System.Data.Objects.DataClasses.EdmScalarPropertyAttribute(EntityKeyProperty=true, IsNullable=false)]
        [global::System.Runtime.Serialization.DataMemberAttribute()]
        public string programCode
        {
            get
            {
                return this._programCode;
            }
            set
            {
                this.OnprogramCodeChanging(value);
                this.ReportPropertyChanging("programCode");
                this._programCode = global::System.Data.Objects.DataClasses.StructuralObject.SetValidValue(value, false);
                this.ReportPropertyChanged("programCode");
                this.OnprogramCodeChanged();
            }
        }
        private string _programCode;
        partial void OnprogramCodeChanging(string value);
        partial void OnprogramCodeChanged();
    }
}

And here is the client side code calling the domain service and entity model.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.Windows.Ria.Data;
using GLADYS.Web.GladysDataLayers;
using GLADYS.Web.GladysServices;


namespace GLADYS
    {
    public partial class uc_AlphabetFilter : UserControl
        {

        //data context for getting the data through the ria service.
        private dscStudents ctx = new dscStudents();




        public uc_AlphabetFilter()
            {
            InitializeComponent();
            //Loaded += new RoutedEventHandler(uc_AlphabetFilter_Loaded);
            ctx.Load(ctx.GetVw_studentAlphabetSetQuery(200980, "BSED-ELED-ED")).Completed += new EventHandler(uc_AlphabetFilter_Completed);            
            }





        void uc_AlphabetFilter_Completed(object sender, EventArgs e)
            {
            foreach (var q in ctx.vw_studentAlphabets)
                {
                uc_AlphaButton btn = new uc_AlphaButton();
                btn.pAlphaLetter = q.LastNameStartsWith;
                btn.PNumber = q.Total.Value;

                myWrapPanel.Children.Add(btn);
                }
            }

This same problem is being asked here, but through a different approach.

Answer 1

When working with views using Entity Framework, make sure the entity key gets set correctly. This is often overlooked since views don’t have primary keys EF tries to infer the key and it is often incorrect. Having an incorrect entity key can result in inconsistent and odd query results.