Entity Framework Throwing Cannot Insert Explicit Value for Identity Column In Table … When IDENTITY_INSERT is set to OFF Error

Question

I am using Microsoft SQL Server 2008 R2 and have three relevant tables: ConvertCarbs, Countries and StateProvinces

Using the EF Power Tools I have Reverse Engineered the Database ( http://msdn.microsoft.com/en-us/data/jj593170.aspx ) and am trying to insert a record into the ConvertCarb table using the Entity Framework.

But, the program is throwing the following error when trying to save the changes:

Cannot insert explicit value for identity column in table 'ConvertCarb' when IDENTITY_INSERT is set to OFF.

Here is the run time code:

var convertCarb = new ConvertCarb();
convertCarb.CountryID = 150;
db.ConvertCarbs.Add(convertCarb);
db.SaveChanges();

Here are the classes from the domain model:

public partial class ConvertCarb
{
    public int ConvertCarbID { get; set; }
    public Nullable<int> CountryID { get; set; }
    public virtual Country Country { get; set; }
}

public partial class Country
{
    public Country()
    {
        this.ConvertCarbs = new List<ConvertCarb>();
        this.Offices = new List<Office>();
    }

    public int CountryID { get; set; }
    public string CountryName { get; set; }
    public virtual ICollection<ConvertCarb> ConvertCarbs { get; set; }
}

public partial class StateProvince
{
    public StateProvince()
    {
        this.Offices = new List<Office>();
    }

    public int StateProvID { get; set; }
    public string StateProvAbbr { get; set; }
    public virtual ConvertCarb ConvertCarb { get; set; }
    public virtual ICollection<Office> Offices { get; set; }
}

There should be no problem doing this insert since the ConvertCarbID is an Identity Column and I have verified this by running a tsql insert on the database directly.

Here is the create code for the tables in the database:

/****** Object:  Table [dbo].[ConvertCarb]    Script Date: 04/11/2014 03:04:24 ******/
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

CREATE TABLE [dbo].[ConvertCarb](
    [ConvertCarbID] [int] IDENTITY(1,1) NOT NULL,
    [CountryID] [int] NULL,
    [StateProvID] [int] NULL,
    [KWH_FT2] [float] NULL,
    [G_KWH] [decimal](18, 4) NULL,
    [NatGas_GJ_M2] [float] NULL,
    [FuelOil_GJ_M2] [float] NULL,
 CONSTRAINT [PK_ConvertCarb] PRIMARY KEY CLUSTERED 
(
    [ConvertCarbID] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]

GO

ALTER TABLE [dbo].[ConvertCarb]  WITH NOCHECK ADD  CONSTRAINT [FK_ConvertCarb_Countries] FOREIGN KEY([CountryID])
REFERENCES [dbo].[Countries] ([CountryID])
GO

ALTER TABLE [dbo].[ConvertCarb] NOCHECK CONSTRAINT [FK_ConvertCarb_Countries]
GO

ALTER TABLE [dbo].[ConvertCarb]  WITH NOCHECK ADD  CONSTRAINT [FK_ConvertCarb_StateProvinces] FOREIGN KEY([ConvertCarbID])
REFERENCES [dbo].[StateProvinces] ([StateProvID])
GO

ALTER TABLE [dbo].[ConvertCarb] NOCHECK CONSTRAINT [FK_ConvertCarb_StateProvinces]
GO


/****** Object:  Table [dbo].[Countries]    Script Date: 04/11/2014 03:04:12 ******/
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

SET ANSI_PADDING ON
GO

CREATE TABLE [dbo].[Countries](
    [CountryID] [int] IDENTITY(1,1) NOT NULL,
    [CountryName] [varchar](255) NULL,
 CONSTRAINT [PK_Countries] PRIMARY KEY CLUSTERED 
(
    [CountryID] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]

GO

SET ANSI_PADDING OFF
GO




/****** Object:  Table [dbo].[StateProvinces]    Script Date: 04/11/2014 03:05:23 ******/
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

SET ANSI_PADDING ON
GO

CREATE TABLE [dbo].[StateProvinces](
    [StateProvID] [int] IDENTITY(1,1) NOT NULL,
    [StateProvAbbr] [varchar](2) NULL,
 CONSTRAINT [PK_StateProvinces] PRIMARY KEY CLUSTERED 
(
    [StateProvID] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]

GO

SET ANSI_PADDING OFF
GO

Here are the mapping classes generated by the EF tool:

public class ConvertCarbMap : EntityTypeConfiguration<ConvertCarb>
{
    public ConvertCarbMap()
    {
        // Primary Key
        this.HasKey(t => t.ConvertCarbID);

        // Properties
        // Table & Column Mappings
        this.ToTable("ConvertCarb");
        this.Property(t => t.ConvertCarbID).HasColumnName("ConvertCarbID");
        this.Property(t => t.CountryID).HasColumnName("CountryID");
        this.Property(t => t.StateProvID).HasColumnName("StateProvID");
        this.Property(t => t.KWH_FT2).HasColumnName("KWH_FT2");
        this.Property(t => t.G_KWH).HasColumnName("G_KWH");
        this.Property(t => t.NatGas_GJ_M2).HasColumnName("NatGas_GJ_M2");
        this.Property(t => t.FuelOil_GJ_M2).HasColumnName("FuelOil_GJ_M2");

        // Relationships
        this.HasOptional(t => t.Country)
            .WithMany(t => t.ConvertCarbs)
            .HasForeignKey(d => d.CountryID);
        this.HasRequired(t => t.StateProvince)
            .WithOptional(t => t.ConvertCarb);

    }
}





public class CountryMap : EntityTypeConfiguration<Country>
{
    public CountryMap()
    {
        // Primary Key
        this.HasKey(t => t.CountryID);

        // Properties
        this.Property(t => t.CountryName)
            .HasMaxLength(255);

        // Table & Column Mappings
        this.ToTable("Countries");
        this.Property(t => t.CountryID).HasColumnName("CountryID");
        this.Property(t => t.CountryName).HasColumnName("CountryName");
    }
}


public class StateProvinceMap : EntityTypeConfiguration<StateProvince>
{
    public StateProvinceMap()
    {
        // Primary Key
        this.HasKey(t => t.StateProvID);

        // Properties
        this.Property(t => t.StateProvAbbr)
            .HasMaxLength(2);

        // Table & Column Mappings
        this.ToTable("StateProvinces");
        this.Property(t => t.StateProvID).HasColumnName("StateProvID");
        this.Property(t => t.StateProvAbbr).HasColumnName("StateProvAbbr");
    }
}

Answer 1

This relationship mapping...

this.HasRequired(t => t.StateProvince)
    .WithOptional(t => t.ConvertCarb);

...means that StateProvince is the principal and ConvertCarb the dependent in a shared primary key one-to-one relationship. In that case EF assumes that only the principal can have an identity primary key, not the dependent ConvertCarb (because the dependent must always have the same PK value as the principal). Basically this relationship disables the identity convention for the ConvertCarb entity. As a result EF sends the PK value (no matter if manually supplied or the default) of the ConvertCarb entity to the database (the ConvertCarbID column is part of the INSERT statement) which throws the database exception because the ConvertCarbID column is marked as identity.

However I don't know why EF picked up that one-to-one relationship from the database since I don't see a FK constraint to StateProvince in your database script. Or has that constraint been added later to the database perhaps?

Answer 2

public class ConvertCarbMap : EntityTypeConfiguration<ConvertCarb>
{
public ConvertCarbMap()
{
    // Primary Key
    this.HasKey(t => t.ConvertCarbID);

    // Properties
    this.HasKey(t => t.ConvertCarbID)
        .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);

    // Table & Column Mappings
    this.ToTable("ConvertCarb");
    this.Property(t => t.ConvertCarbID).HasColumnName("ConvertCarbID");
    this.Property(t => t.CountryID).HasColumnName("CountryID");
    this.Property(t => t.StateProvID).HasColumnName("StateProvID");
    this.Property(t => t.KWH_FT2).HasColumnName("KWH_FT2");
    this.Property(t => t.G_KWH).HasColumnName("G_KWH");
    this.Property(t => t.NatGas_GJ_M2).HasColumnName("NatGas_GJ_M2");
    this.Property(t => t.FuelOil_GJ_M2).HasColumnName("FuelOil_GJ_M2");

    // Relationships
    this.HasOptional(t => t.Country)
        .WithMany(t => t.ConvertCarbs)
        .HasForeignKey(d => d.CountryID);
    this.HasRequired(t => t.StateProvince)
        .WithOptional(t => t.ConvertCarb);

}
}

Use DatabaseGeneratedOption.Identity in HasDatabaseGeneratedOption.