CODEWITHSUNDEEP
c#asp.net-mvcentity-framework
Eric
Eric

Reputation: 359

MVC Seed does not put data in the database

I have two tables with a relation between them.

Here are my models:

public  class Locations
{
  [Key]
  public int LocationID { get; set; }

  [Required(ErrorMessage = "This field is required!")]
  [MaxLength(50, ErrorMessage = "The name is too long. Max. 50 characters allowed!")]
  [Display(Name = "Location name:")]
  public string Name { get; set; }

  public int Position { get; set; }

  public virtual LocationType LocationType { get; set; }

}

and

public class LocationType
{
  [Key]
  public int LocationTypeID { get; set; }

  [Required(ErrorMessage = "This field is required!")]
  [MaxLength(25, ErrorMessage = "The name is too long. Max. 25 characters allowed!")]
  [Display(Name = "Location type:")]
  public string Name { get; set; }

  public int Position { get; set; }

  public int HasChoicesOrInput { get; set; } 

  public virtual ICollection<Locations> Locations { get; set; }
}

In my configuration.cs file I have the following seed:

context.LocationType.AddOrUpdate(a => a.LocationTypeID,
  new LocationType
  {
    Name = "AAAAA",
    HasChoicesOrInput = 1,
    Position = 1,
    Locations = { new Locations { Name = "1111111", Position = 1 },
                    new Locations { Name = "2222222", Position = 2 }
                }
  });

Table definition:

CREATE TABLE [dbo].[Locations] (
[LocationID]                  INT           IDENTITY (1, 1) NOT NULL,
[Name]                        NVARCHAR (50) NOT NULL,
[Position]                    INT           NOT NULL,
[LocationType_LocationTypeID] INT           NULL,
CONSTRAINT [PK_dbo.Locations] PRIMARY KEY CLUSTERED ([LocationID] ASC),
CONSTRAINT [FK_dbo.Locations_dbo.LocationTypes_LocationType_LocationTypeID] FOREIGN KEY ([LocationType_LocationTypeID]) REFERENCES [dbo].[LocationTypes] ([LocationTypeID])
);

CREATE TABLE [dbo].[LocationTypes] (
[LocationTypeID]    INT           IDENTITY (1, 1) NOT NULL,
[Name]              NVARCHAR (25) NOT NULL,
[Position]          INT           NOT NULL,
[HasChoicesOrInput] INT           NOT NULL,
CONSTRAINT [PK_dbo.LocationTypes] PRIMARY KEY CLUSTERED ([LocationTypeID] ASC)
);

When I do an Update-Database, I get an "Object reference not set to an instance of an object." error.

Why? The tables exist in the database, the relation too. What am I missing here?

Upvotes: 1

Views: 61

Answers (1)

Jakub Lortz
Jakub Lortz

Reputation: 14896

The Locations intializer

new LocationType
{
  Name = "AAAAA",
  HasChoicesOrInput = 1,
  Position = 1,
  Locations = { new Locations { Name = "1111111", Position = 1 },
                new Locations { Name = "2222222", Position = 2 }
            }
});

does not create a Locations collection. It calls the property getter to get the existing Locations collection and calls Add on it. Since you never assigned anything to that property, you get the NullReferenceException.

This syntax is described in C# language specification, section 7.6.10.2 Object initializers:

A member initializer that specifies a collection initializer after the equals sign is an initialization of an embedded collection. Instead of assigning a new collection to the field or property, the elements given in the initializer are added to the collection referenced by the field or property. You should create a new instance of a collection (for example a list or an array) and assign it to Locations property in the initializer:

new LocationType
{
  Name = "AAAAA",
  HasChoicesOrInput = 1,
  Position = 1,
  Locations = new List<Locations> 
  { 
      new Locations { Name = "1111111", Position = 1 },
      new Locations { Name = "2222222", Position = 2 }
  }
});

Upvotes: 3

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