Linq to sql class error: must add reference to assembly Syste.data.linq

Question

I created .Net Framework web form app in VS 2019 community. I added linq tosql class (dmbl) using table from AdventureWorks CountryRegions table. The class was created successfully . However I get error in my Business class (Bal): Error says:
CS0012 The type 'Table<>' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Data.Linq, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.
I can see System.Data.Linq added to the references.
And System.Linq in Nuget packages.

using Microsoft.Owin;
using Owin;
using System;
using System.Threading.Tasks;
//using System.Data.Common

using System.Linq;
using System.Collections.Generic;

//[assembly: OwinStartup(typeof(OBjectDSDemo.App_Code.Biz.Bal))]

namespace OBjectDSDemo.App_Code.Biz
{
    public class Bal
    {
        public List<CountryRegion> GetCustomers()

        {
            var contxt = new DataClasses1DataContext();

            //customers=from c in 

            return (from c in contxt.CountryRegions select c.Country).toList();

        }
    }
}

#pragma warning disable 1591
//------------------------------------------------------------------------------
// <auto-generated>
//     This code was generated by a tool.
//     Runtime Version:4.0.30319.42000
//
//     Changes to this file may cause incorrect behavior and will be lost if
//     the code is regenerated.
// </auto-generated>
//------------------------------------------------------------------------------

namespace OBjectDSDemo
{
    using System.Data.Linq;
    using System.Data.Linq.Mapping;
    using System.Data;
    using System.Collections.Generic;
    using System.Reflection;
    using System.Linq;
    using System.Linq.Expressions;
    using System.ComponentModel;
    using System;


    [global::System.Data.Linq.Mapping.DatabaseAttribute(Name="AdventureWorks")]
    public partial class DataClasses1DataContext : System.Data.Linq.DataContext
    {

        private static System.Data.Linq.Mapping.MappingSource mappingSource = new AttributeMappingSource();

    #region Extensibility Method Definitions
    partial void OnCreated();
    partial void InsertCountryRegion(CountryRegion instance);
    partial void UpdateCountryRegion(CountryRegion instance);
    partial void DeleteCountryRegion(CountryRegion instance);
    #endregion

        public DataClasses1DataContext() : 
                base(global::System.Configuration.ConfigurationManager.ConnectionStrings["AdventureWorksConnectionString"].ConnectionString, mappingSource)
        {
            OnCreated();
        }

        public DataClasses1DataContext(string connection) : 
                base(connection, mappingSource)
        {
            OnCreated();
        }

        public DataClasses1DataContext(System.Data.IDbConnection connection) : 
                base(connection, mappingSource)
        {
            OnCreated();
        }

        public DataClasses1DataContext(string connection, System.Data.Linq.Mapping.MappingSource mappingSource) : 
                base(connection, mappingSource)
        {
            OnCreated();
        }

        public DataClasses1DataContext(System.Data.IDbConnection connection, System.Data.Linq.Mapping.MappingSource mappingSource) : 
                base(connection, mappingSource)
        {
            OnCreated();
        }

        public System.Data.Linq.Table<CountryRegion> CountryRegions
        {
            get
            {
                return this.GetTable<CountryRegion>();
            }
        }
    }

    [global::System.Data.Linq.Mapping.TableAttribute(Name="Person.CountryRegion")]
    public partial class CountryRegion : INotifyPropertyChanging, INotifyPropertyChanged
    {

        private static PropertyChangingEventArgs emptyChangingEventArgs = new PropertyChangingEventArgs(String.Empty);

        private string _CountryRegionCode;

        private string _Name;

        private System.DateTime _ModifiedDate;

    #region Extensibility Method Definitions
    partial void OnLoaded();
    partial void OnValidate(System.Data.Linq.ChangeAction action);
    partial void OnCreated();
    partial void OnCountryRegionCodeChanging(string value);
    partial void OnCountryRegionCodeChanged();
    partial void OnNameChanging(string value);
    partial void OnNameChanged();
    partial void OnModifiedDateChanging(System.DateTime value);
    partial void OnModifiedDateChanged();
    #endregion

        public CountryRegion()
        {
            OnCreated();
        }

        [global::System.Data.Linq.Mapping.ColumnAttribute(Storage="_CountryRegionCode", DbType="NVarChar(3) NOT NULL", CanBeNull=false, IsPrimaryKey=true)]
        public string CountryRegionCode
        {
            get
            {
                return this._CountryRegionCode;
            }
            set
            {
                if ((this._CountryRegionCode != value))
                {
                    this.OnCountryRegionCodeChanging(value);
                    this.SendPropertyChanging();
                    this._CountryRegionCode = value;
                    this.SendPropertyChanged("CountryRegionCode");
                    this.OnCountryRegionCodeChanged();
                }
            }
        }

        [global::System.Data.Linq.Mapping.ColumnAttribute(Storage="_Name", DbType="NVarChar(50) NOT NULL", CanBeNull=false)]
        public string Name
        {
            get
            {
                return this._Name;
            }
            set
            {
                if ((this._Name != value))
                {
                    this.OnNameChanging(value);
                    this.SendPropertyChanging();
                    this._Name = value;
                    this.SendPropertyChanged("Name");
                    this.OnNameChanged();
                }
            }
        }

        [global::System.Data.Linq.Mapping.ColumnAttribute(Storage="_ModifiedDate", DbType="DateTime NOT NULL")]
        public System.DateTime ModifiedDate
        {
            get
            {
                return this._ModifiedDate;
            }
            set
            {
                if ((this._ModifiedDate != value))
                {
                    this.OnModifiedDateChanging(value);
                    this.SendPropertyChanging();
                    this._ModifiedDate = value;
                    this.SendPropertyChanged("ModifiedDate");
                    this.OnModifiedDateChanged();
                }
            }
        }

        public event PropertyChangingEventHandler PropertyChanging;

        public event PropertyChangedEventHandler PropertyChanged;

        protected virtual void SendPropertyChanging()
        {
            if ((this.PropertyChanging != null))
            {
                this.PropertyChanging(this, emptyChangingEventArgs);
            }
        }

        protected virtual void SendPropertyChanged(String propertyName)
        {
            if ((this.PropertyChanged != null))
            {
                this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }
    }
}
#pragma warning restore 1591

Answer 1

thanks Xudong it works. I only needed to restart visual studio

Answer 2

Hi @kobosh ,

According to your description, I did some related searches on this issue.

And here is a similar case, you could try:

• Navigate to the web project's References node
• Find the reference to System.Data.Linq
• Open the VS Properties Window
• In the properties window, change Copy Local: False to True

Or you could try copy the System.Data.Linq dll reference to bin directory.

Best regards,
Xudong Peng

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Answer 3

thanks Xudong it works. I only needed to restart visual studio