Scripting EF 4.3 code-first database via ObjectContext fails, while creating via built-in DatabaseInitializer succeeds

Question

I want to programmatically create the database create script for my EF 4.3 Code-First database. The database creates just fine using the standard DatabaseInitializer mechanisms, but the following code fails:

using(var dc = new MyContext())
{
    var objContext = (IObjectContextAdapter)dc;
    var script = objContext.ObjectContext.CreateDatabaseScript();
}

The exception I get is:

The store generated pattern 'Computed' is not supported for properties that are not of type 'timestamp' or 'rowversion'.

I do have a Computed column defined of type "string" but like i said, the database creates fine when created via the built-in DatabaseInitializer. Oddly enough, the resulting schema using this method doesn't actually create a computed column.

As to why I'm doing this, I have a script that runs post-create that drops this column and creates a bonafide computed column. Without specifying the column as computed in the EF mapping, it will attempt to assign that column a value upon inserts, which then fails.

Arthur Vickers · Accepted Answer · 2012-05-31 21:16:54Z

1

Leaving database creation aside for a moment, setting “Computed” means that EF will not attempt to write the value of that column but will read the value that was (presumably) computer by the server each time the column is queried. From an EF perspective it is valid to have a computed column for any data type.

Now consider database creation from the EF model. EF doesn’t know what to do to create the computed column in the database, and indeed it may not even be possible to do it without triggers in certain databases depending on the type of the column. So in EF4 the decision was made to make CreateDatabaseScript throw in these situations.

However, EF 4.3 and later don’t use CreateDatabaseScript anymore when targeting SQL Server or SQL Server Compact. They instead use the Migrations pipeline. For the Migrations pipeline we decided to take a different approach because we felt that it was wrong for database creation to always throw for what could be a perfectly valid model. Especially considering you could have written your own SQL in the migration that added a trigger or some other mechanism to make the database create a valid computed column.

So this is why you see the database being created by EF 4.3 (but without doing anything to make the column computed) but then you see the same model throw when trying to use CreateDatabaseScript which uses the older, non-Migrations mechanisms.

The way to fix this is to have Migrations create the scripts instead of using CreateDatabaseScript.

answered May 31, 2012 at 21:16

Arthur Vickers

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1 Comment

w.brian Over a year ago

I've been at odds with Migrations as you can see by some of my recent questions. The dependence on an actual database is problematic. For reasons beyond my control, I require the ability to simply get the DDL scripts, whether it's a "diff" script from one migration to another or the entire create script at any given point.

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