Entity Framework DbSet throws NullReferenceException

Question

I try to post some values into my mysql database with the entity framework. I'm able to connect to my database successfully. But, after I try to add some values, I've got an NullReferenceException error.

Here's my code:

public class MysqlContext: DbContext
{
    public DbSet<Test> Test { get; set; }

    public MysqlContext(): base("MysqlDefaultConnection")
    {
        Database.Connection.Open();
        var t = new Test { Name = "test", Id = 0 };
        Test.Add(t);
        SaveChanges();
    }
}

[Table("test")]
public class Test
{
    [Key]
    public int Id { get; set; }
    public string Name { get; set; }
}

And this is my configuration of my entity framework:

<configSections>
<section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
</configSections>

<connectionStrings>
<add name="MysqlDefaultConnection" connectionString="server=localhost;user id=dev;password=****;database=****" providerName="MySql.Data.MySqlClient" />

<entityFramework>
<defaultConnectionFactory type="MySql.Data.Entity.MySqlConnectionFactory, MySql.Data.Entity.EF6" />
<providers>
  <provider invariantName="MySql.Data.MySqlClient" type="MySql.Data.MySqlClient.MySqlProviderServices, MySql.Data.Entity.EF6" />
</providers>

Finally this is my table description from my database:

CREATE TABLE `test` (
`Id` int(11) NOT NULL AUTO_INCREMENT,
`Name` varchar(45) NOT NULL,
PRIMARY KEY (`Id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8

So, if I try to connect to my database, everything is okay. After I try to add my entity into the DbSet I'll get an exception.

I've got the error here: "Test.Add(t);". And here is my stacktrace: pastebin.com/B2yd64Ff — user3149497
– user3149497, Commented Sep 6, 2015 at 11:00
You don't give the context any chance to initiate its own Properties before running your code. It's only just constructing. This is not the right place to put such code. It doesn't even belong anywhere inside the context class. — Gert Arnold
– Gert Arnold, Commented Sep 6, 2015 at 19:40

3615 · Accepted Answer · 2015-09-06 14:34:29Z

1

It behaves the same way if you try this code not in the DbContext constructor?

public class MysqlContext: DbContext
{
    public DbSet<Test> Test { get; set; }

    public MysqlContext(): base("MysqlDefaultConnection")
    {

    }
}

[Table("test")]
public class Test
{
    [Key]
    public int Id { get; set; }
    public string Name { get; set; }
}

public void Main()
{
  var myContext = new MysqlContext();
  var t = new Test { Name = "test", Id = 0 };    
  myContext.Set<Test>.Add(t);
  myContext.SaveChanges();
}

edited Sep 6, 2015 at 14:34

answered Sep 6, 2015 at 11:23

3615

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Comments

Devon Burriss · Accepted Answer · 2015-09-06 11:33:07Z

0

I believe this is because you are doing this in the contractor. At this stage I would assume Test property is not initialised to a value yet. Try run your test code later in the application lifecycle after MysqlContext has been initialized.

answered Sep 6, 2015 at 11:33

Devon Burriss

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1 Comment

user3149497 Over a year ago

Okay, I've created a new method, within I'll add the entity into the database. But still, I'll become the same error as before.

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