在 EF4 中自动创建数据库的问题

Question

I'm learning ASP.NET MVC 3 with Entity Framework Code First. I'm following a tutorial and I downloaded the corresponding solution for testing on my local machine. Now, something I didn't understand very well is about the automatic creation of the database (if this one didn't exist yet on disk). The very first time I run the application, the database is created for me. That's ok.

Here is the section in Web.config

<add name="BlogContext" 
     connectionString="Data Source=.\SQL2008;Initial Catalog=CodeFirstMVC.mdf;Integrated Security=SSPI"
     providerName="System.Data.SqlClient" /> 

But I have two problems:

1st. For testing purpose, I deleted the database on disk and run again the solution. I thought that the database would be automatically created but I was wrong: I got the error message below:

{"Unable to open the physical file \"c:\\Program Files\\Microsoft SQL Server\\MSSQL10.SQL2008\\MSSQL\\DATA\\CodeFirstMVC.mdf.mdf\". Operating system error 2: \"2(failed to retrieve text for this error. Reason: 15105)\".\r\nCannot open database \"CodeFirstMVC.mdf\" requested by the login. The login failed.\r\nLogin failed for user 'sa'.\r\nFile activation failure. The physical file name \"c:\\Program Files\\Microsoft SQL Server\\MSSQL10.SQL2008\\MSSQL\\DATA\\CodeFirstMVC.mdf_log.LDF\" may be incorrect."}

I noticed that if I changed the file name in my Web.config then the database is again successfully created. Can you explain me? Why do I have to change the database name to get it running again?

2nd. The database is created in the folder located in C:\Program Files\Microsoft SQL Server\MSSQL10.SQL2008\MSSQL\DATA. I would like to store my database in the App_Data directory. How can I proceed?

Answer 1

Initial catalog is not path to file. It is the name of database. AttachDbFilename is used to specify the file so your connection string should look like:

Data Source=.\SQL2008;Initial Catalog=CodeFirstMVC;AttachDbFilename=|DataDirectory|CodeFirstMVC.mdf;Integrated Security=SSPI

Where |DataDirectory| instructs SQL server to use local application data directory instead of global SQL Server data directory. Local data directory for web application is App_Data .

Edit:

I just noticed that you are probably using full SQL server instead of SQL server express. As I know creating database in App_Data automatically is feature of SQL server express. That also explains first error because SQL server created database called CodeFirstMVC.mdf and stored the database in its global data directory within CodeFirstMVC.mdf.mdf file and transaction log in CodeFirstMVC.mdf.ldf file. It also registered that database internally. By deleting files you didn't remove database from SQL server. You just break its functionality but SQL server still believes that the database exists. That is also reason why you have to change the name to make it work.