I am working on a new application in .Net 5 using EF Core. After creating some entity classes and doing the first few migrations I discovered that I wanted to change the data type of column and make it the key in one of the tables. I was able to do that without issue and the app works just fine with that change - but now if I try to change anything else in that table like add a new column and do a migration I get the following error: "To change the IDENTITY property of a column, the column needs to be dropped and recreated." I have tried even dropping the entire table - but nothing seems to work.
Whenever your migrations get messed up, especially early in a project, just delete the migrations folder, drop the Migration History table and start fresh with a new initial migration.
Related
Recently i upgraded from EF5 to EF6 and here is list of items which one needs to take care of
EF MiniProfiling: if you were using mini profiling with EF5 you will have broken code as few of the functiionality or variable names had been changed.
Resolution: Upgrade to newer version of EF MiniProfiling
Db-Reindexing: After updating to EF6 it complaints you about change in your model and when you do "Add-Migration" you will see all your index for primary key were getting recreated also its changing name of tables where you have one to one relationship so previously if it generates table name as TableATableB then it will rename table as TableBTableA dont know why.
Resolution 1: Let EF create migrations for create index , just comment out line in
up and down function.
Resolution 2: Copy line of code from down function(i.e. drop index) and try to execute it before it create index , simple rule first drop and then create, you need this else EF will complaint about index already present.
Migrations: This will only affect you if you are doing using some tool to deploy you assemblies and which in turns uses migrate.exe typically found at
...#your project location\packages\EntityFramework.6.1.0\tools\migrate.exe
copy it to your bin folder and things should work fine.
4. Null Handling: In EF6 handling of null values had been changed , my hands on experience says that with ef5 select query was ignoring null cases but is not the case with ef6
e.g. if i have query something like
db.context.entity.where(name != "ab");
and lets say entity table contains two names {"ab",null}
with EF5 it will return 1 row with ef6 it was returning 2 rows
http://entityframework.codeplex.com/workitem/2115
Resolution: If you wanted to work exactly like EF5 you can set
dbContext.Configuration.UseDatabaseNullSemantics = true;
If it helps please don't forgot to mark this post as answered :)
My application uses Entity Framework 5.0 code-first on top of a Sql CE database. Until now, we have used Automatic Migrations to manage entity mapping changes. However, I now have a change for which I need to create a custom migration to ensure no data is lost during the update. I made my changes to the entities, and used the Add-Migration command which generated Up() and Down() methods for me. I customized the Up() method to insert my custom sql to preserve the data, and tested my application.
When I run the application, I received the error:
Unable to update database to match the current model because there are pending changes and automatic migration is disabled. Either write the pending model changes to a code-based migration or enable automatic migration. Set DbMigrationsConfiguration.AutomaticMigrationsEnabled to true to enable automatic migration.
Ok, I don't understand this because all of my changes are detailed in the Up() method that got executed.
So I turn Automatic Migrations back on just to see what happens. Now I receive this error:
"Cannot alter column of type NTEXT or IMAGE [ Column Name = LastName ]"
This error comes from a table/entity that hasn't even been touched with my changes. The existing database has this string mapped to nvarchar(4000). If I examine the DB after I receive this exception, I observe that the columns have been changed to ntext. What is EF doing? Why is it touching tables that haven't been changed? How can I get more information on what is going on here?
Update:
As a workaround, I attempted to mark each and every string type in my entities with a data annotation as such:
[Column(TypeName = "ntext")]
public virtual string LastName
{
get;
set;
}
Now all of my strings are using ntext in the database. This leads to further exceptions when queries are performed:
The ntext and image data types cannot be used in WHERE, HAVING, GROUP BY, ON, or IN clauses, except when these data types are used with the LIKE or IS NULL predicates.
So, to summarize:
Turning off automatic migrations causes EF to detect phantom changes and throw exceptions
Turning on automatic migration in conjunction with a custom migration causes all existing strings to be mapped to ntext
strings mapped to ntext cannot be queried, effectively making them useless in my application
For me, a modification of an Up method worked out.
SerialNumber = c.String(maxLength: 99)
was applied instead of
SerialNumber = c.String()
i had the same issue and i fixed by editing the table column data type manually by opening SQl Server Compact/SQlite Toolbox explorer windows, and then expend the database name, then expend the table you want to edit and right click the column you want to edit, and click drop script, then run the scrip and the column will be dropped from the table, then right click the table and click add column and from here you can choose what data type you want and add the new column that way. I hope this helps some one.
Now i'm using EF6 Alpha, and when using migration, it will add a new migration log into the __MigrationHistory table.
In EF6, The __MigrationHistory table has a new column called "ContextKey". After testing, I found there are two default "ContextKey" value:
The full name of DbContext's derived class.This happens when i run the code:
Database.CreateIfNotExists();
The full name of DbMigrationsConfiguration's derived class. This happens when i run the code:
public ArticleDbContext()
{
Database.SetInitializer(new MigrateDatabaseToLatestVersion<ArticleDbContext, ArticleConfiguration>());
}
The first time i run the application, "Database.CreateIfNotExists();" create a new database for me, also all tables that map to the models defined in ArticleDbContext, and then add a __MigrationHistory row which ContextKey's value is "Module.Article.Model.ArticleDbContext".
And then "Database.SetInitializer(new MigrateDatabaseToLatestVersion());" will be runned, this code will generate a new ContextKey "PowerEasy.Module.Article.Migrations.ArticleConfiguration". Migration query the __MigrationHistory table with this ContextKey and find out there's no data. So again it will create all tables that map to the models defined in ArticleDbContext, but the tables are already exist in the database, so an exception will be throwed, and tell me "the table XXX is already existed".
How can i solve this?
You should not mix Migrations and the Database.CreateIfNotExists method (or any of the initializers built on top of it). Migrations will take care of creating the database if it does not already exist.
As an alternative to the Migrations initializer, you can also apply migrations using the DbMigrator.Update method. This is useful if you want to create/update the database before it would otherwise be triggered by the initializer.
I am using Entity Framework 5 RC, code first. I am struggling with migrating databases that were created on different versions of code. For example, Database A was created when table FooBar didn't exist. Database B was created after table FooBar was added to my model.
I have a migration written that adds the FooBar table. Is it my responsibility to check in the FooBar migration that the table doesn't exist before calling CreateTable? It seems that is the case since Database B doesn't have an entry for the FooBar migration and will attempt to run it.
At first the MigrationHistory table seemed like it would save me from adding these checks but since new databases won't have entries for migrations added before the database was created, I still need to do the checks myself. Is that the right way to go about it or am I missing something?
To get around an issue I had with adding Stored Procedures, I wrote a TSQL script to create a new table "_PreviousMigrationHistory" - which receives new entries from the "_MigrationHistory" table after my stored procedure scripts have run...
I did add a new column to both tables ( "VersionId", of INT - IDENTITY(1,1) ) which is what I use for comparison within my code.
This way you have the un-updated migration patterns available to you (__PreviousMigrationHistory), even after Code First Migrations have occurred.
Would this help?
**EDIT - sorry, I miss read the question. - Although I would think that new instances of the database would still go through the migration steps, which in turn should add the entries to the __MigrationHistory table?
I've tried using Entity Framework Code First and set AutomaticMigrationsEnabled to true so that when I change the model classes the database would automatically update.
Then I have a table, where I added length to one field. Example
Employee.Firstname(50) -> Employee.Firstname(100). The updated was successful.
But I have entered wrong data so I want to reset the database so I execute:
update-database -targetmigration:"0" -force -verbose
But I got the ff error:
System.Data.SqlClient.SqlException (0x80131904): String or binary data would be truncated.
Currently, my solution is to delete all the tables in the database manually as well as delete all the records in __MigrationHistory, then reinstall the EntityFramework.Migrations via NuGet.
Is there an easy way to do it?
I've solved this problem by updating to EntityFramework.Migrations version 0.8.0.0.0.