How do I access the elmah database from code?

Question

VS2013 update 4, MVC5, elmah.mvc (same as elmah), VB/C#

The following code is part of the standard MVC template to get started and it is part of setting up our database connection from within code to access an SQL database:

Public Class ApplicationDbContext
  Inherits IdentityDbContext(Of ApplicationUser)
  Public Sub New()
    MyBase.New("DefaultConnection", throwIfV1Schema:=False)
    Me.Configuration.LazyLoadingEnabled = True
  End Sub

  Public Shared Function Create() As ApplicationDbContext
    Return New ApplicationDbContext()
  End Function

We also need the following or something similar in web.config:

<configuration>
  <connectionStrings>
    <add name="DefaultConnection" connectionString="Data Source=mypc\SQLEXPRESS;Initial Catalog=mydb.DefaultContext;Integrated Security=True" providerName="System.Data.SqlClient" />
    <add name="ElmahConnection" connectionString="Data Source=mypc\SQLEXPRESS;Initial Catalog=mydb.elmah;Integrated Security=True" providerName="System.Data.SqlClient" />
  </connectionStrings>

I added the elmah connection string as it is relevant to my question.

Then in each location where needed, the following definition is added and we can access the database tables using db.< tablename>...:

Private db As New ApplicationDbContext

I want to write some methods to work with and on the elmah data table but it is a different context than ApplicationContext. I don't quite understand what I would write to setup a connection to the elmah table since I didn't really set that up, it came in the dll for elmah.

Answer 1

While keeping error records makes sense, during development I wanted to clear the Elmah log. While probably trivial for most, it was a good exercise to figure it out. I was so used to code first, I forgot EF also does database first.

In VS2013 update 4 the following Wizard made this task pretty easy.

1) Project > Add New Item > Data > ADO.NET Entity Data Model

2) Give the model a name (With great creativity I used 'elmah') > Click Add

3) This is where it gets pretty cool. I'm not sure when it was added but the EF framework now includes a new choice called Code First From Database. Click on that.

4) Select the elmah connection string

Note: There is an option to save connection settings in web.config. That simply creates a duplicate connection string. Leave it checked or don't, but using the existing string is fine. I didn't select the option and web.config was left untouched. However, not using that option means the connection string name will have to be updated in the context definition > Click Next

5) Click on Tables to load the Elmah table, leave the defaults as is > Click Finish

The wizard creates 2 files and places them in the project. One is named by the data table name which is ELMAH_Error; this is the model. The other is a parital class that sets up the context. If the save connection option was selected then web.config will be modified to add the new connection string. Note: I combined the 2 Classes into a single file for convenience (may require adding some Using or Imports) and the Public Sub New() is where the connection string name must be updated if the existing connection string is used as shown below.

Partial Public Class elmah
  Inherits DbContext

  Public Sub New()
    MyBase.New("name=ElmahConnection")
  End Sub

  Public Overridable Property ELMAH_Error As DbSet(Of ELMAH_Error)

  Protected Overrides Sub OnModelCreating(ByVal modelBuilder As DbModelBuilder)
  End Sub
End Class

6) With all that automatically done (except for the connection string name if required), all that is required is to write the desired code. I wanted to empty the elmah log from time to time and used the following:

Public Class ErrorController
  Inherits Controller

  Private db1 As New elmah

Function DeleteElmahRecords() As ActionResult

  Dim elmahTable = db1.ELMAH_Error.ToList()
  db1.ELMAH_Error.RemoveRange(elmahTable)
  db1.SaveChanges()

  Return RedirectToAction("ErrorTesting")
End Function
…
End Class

Obviously I have a method called ErrorTesting that the function returns to and I access this method from a link on that same page.

Hope this is useful for someone. It's kind of the only way I can give back considering the awesome guru help I often get from this site.