Error saving data in SQL Server

The problem is that the column código does not support values null , most likely this column is the primary key of your table or a unique key.

What you should do to fix it is assign a value to this column.

Or better yet, before trying to insert the values in the database, check if the assigned values are correct and if not, show the appropriate messages to the user.

Update:

As I said, you have to make sure that the property Código has a value before calling the database to get two things:

This can be implemented in many ways. A simple way to do this could be to convert your method into a function that returns a booleano if the data has been saved and a list of the errors to be displayed to the user.

The code could be something like (beware that I am from C # and I used the Telerik converter for this code )

Public Shared Function AGREGARPROVEEDOR(codigo As String, _
    nombres As String, _
    apellidos As String, _
    direccion As String, _
    ciudad As String, _
    telefono As String, _
    ByRef errores As String()) As Boolean

    errors = New List(Of String)()

    ' Comprobar 
    If String.IsNullOrEmpty(codigo) Then
        errors.Add("Debe establecer el código del proveedor.")
    End If

    'TODO: Realizar otras comprobaciones

    ' Salir en caso de no pasar las validaciones
    If errors.Count > 0 Then
        Return False
    End If

    Using BD As New SCXPEntities1()
        BD.PROVEEDORES.AddObject(New PROVEEDORE() With { _
            Key .CODIGO = codigo, _
            Key .NOMBRES = nombres, _
            Key .APELLIDOS = apellidos, _
            Key .DIRECCION = direccion, _
            Key .CIUDAD = ciudad, _
            Key .TELEFONO = telefono _
        })
        BD.SaveChanges()
    End Using
    Return True
End Function

Another way to solve it would be using the validation engine provided by the Entity Framework itself as explained in this article (in English)

The same error message describes the situation:

  

"Unable to insert the NULL value in the 'CODE' column, table   dbo.PROVEEDORES "

You can modify the 'CODE' column of your SUPPLIERS table so that it accepts null values by means of a script by means of Alter Table .

Or modify directly in SQL Server the property to accept nulls from your field''CODIGO'' by selecting the attribute " Allow Nulls ":

You could use the example so that you also have an idea for when it does not let you use NULL values, I always do them in the query; Here is an example of how I did it:

create procedure SP_MANTENMENT_RUTA @ INT OPERATION, @ CODE INT, @Localidad_Rt varchar (150), @Description_Rt varchar (150), @SubRuta bit, @Estate_Rt bit, @LimiteCredit decimal (18.2) ACE BEGIN

SET NOCOUNT ON;
-- INSERT
IF @OPERACION = 1
BEGIN
DECLARE @MAXIMO INT
SET @MAXIMO = (SELECT MAX(ISNULL(Ruta_ID,0)) + 1 AS MAXIMO FROM Logic_Ruta)
    INSERT INTO Logic_Ruta(Ruta_ID,Localidad_Rt, Descripciòn_Rt, SubRuta, Estado_Rt, LimiteCreditRuta)
        values (@MAXIMO,@Localidad_Rt,@Descripcion_Rt,@SubRuta,@Estado_Rt, @LimiteCreditRuta )
END
--Actualiza
IF @OPERACION = 2
BEGIN
    UPDATE Logic_Ruta SET Localidad_Rt = @Localidad_Rt, Descripciòn_Rt = @Descripcion_Rt,SubRuta =@SubRuta, Estado_Rt = @Estado_Rt, LimiteCreditRuta= @LimiteCreditRuta
        WHERE Ruta_ID = @CODIGO
END
--CARGA GRID
IF @OPERACION = 3
BEGIN
SELECT Ruta_ID AS CODIGO,Localidad_Rt AS Localidad_Rt, Descripciòn_Rt AS Descripcion_Rt, SubRuta AS SubRuta, Estado_Rt as Estado_Rt, LimiteCreditRuta AS LimiteCreditRuta
     FROM Logic_Ruta
END

END