I'm trying to use migrations to add a parent table to an existing child table. For eg. I currently have User table, now I want to add a Department table that has a 1 to many relationship: Department has many User.
My questions, in automatic update, can I somehow seed the parent table before adding the FK so I can update all the children to this default seeded Department? If automatic update cannot do this, how do I accomplish this in code?
What I currently did: Made the FK nullable, created the Parent and seeded it, then update all child User FK to the parent. But now I cant change the FK not nullable because throws this error: Automatic migration was not applied because it would result in data loss.
Switching from nullable to non-nullable is considered data loss because after the migration, there is no way to tell which rows (if any) were null. If you are ok with this, you can call Update-Database with the -Force flag.
Another option would be to add a code-based migration that would:
Add the Departments table
Insert a default department
Add the required FK column to User with a default value of the inserted department
Related
Some of my entities have navigation properties as they have a foreign key to another entity in the database. In my code, I've set the primary keys of the navigation properties to link the entities with each other.
The problem is that entity framework sees this as a new entity and tries to add it to the database with next error as a result:
Cannot insert explicit value for identity column in table 'xxx' when IDENTITY_INSERT is set to OFF.
Obviously, because the entity is new and not acquired from the database.
Is there a way in EF to remove the tracking of the entity?
We are trying to implement a multi tenant architecture in our Web API based application. We are using RLS in SQL Server, and Subscription_Id is, what is given to each subscriber. We have set the default value for Subscription_Id in SQL Server, so while I am calling db.SaveChanges(), I just want to ignore the Subscription_Id going to the SQL Server from the API.
I tried setting the value of Subscription_Id in the SaveChanges() override method but got stuck here.
public override int SaveChanges()
{
var objectType = selectedEntity.CurrentValues.ToObject();
Guid value = new Guid("54E720FC-616B-44C6-8485-5F2185FD7B4C");
PropertyInfo propertyInfo =
objectType.GetType().GetProperty("Subscription_Id");
ChangeTracker.Entries().FirstOrDefault()
.CurrentValues.ToObject().GetType()
.GetProperty("Subscription_Id")
.SetValue(objectType, Convert.ChangeType(value, propertyInfo.PropertyType), null);
return base.SaveChanges();
}
My advice is that you shouldn't modify your SaveChanges() code for this.
A recommended way of using RLS is making the TenantId columns transparent to your EF model and your code, so you don't need to define Tenant ID or navigation properties in your entities. This way you don't need to change your SaveChanges() code, or to explicitly manage and set Subscription_Id values anywhere in your code other that when opening the DB connection.
What you need to do is manually setting a default value constraint in the Subscription_Id columns in your database, with a default value based on the current session Subscription_Id parameter. The value will be set when inserting the records, and implicitly used to filter any subsequent queries and commands at database level.
In case of a new column:
ALTER TABLE SomeEntityTable ADD Subscription_Id nvarchar(128)
DEFAULT CAST(SESSION_CONTEXT(N'UserId') AS nvarchar(128))
In case of an existing column:
ALTER TABLE SomeEntityTable
ADD DEFAULT CAST(SESSION_CONTEXT(N'UserId') AS nvarchar(128)
FOR Subscription_Id
If the column had a previous different DEFAULT value it would be good to also delete its associated obsolete DEFAULT constraint. More info about updating default values in existing columns can be found here.
These columns should not be included in your model. You should not have properties for them in your entity classes. If you are using Database First you should make sure you exclude/ignore these columns when updating your model from your database.
How to do this if you are using EF Code First: you can manually include AlterColumn (or CreateColumn) instructions in a code migration after you generate it with Add-Migration. Do it for every entity table:
public override void Up()
{
AlterColumn("dbo.SomeEntityTable", "Subscription_Id",
c => c.String(
nullable: false,
maxLength: 128,
defaultValueSql: "CAST(SESSION_CONTEXT(N'UserId') AS nvarchar(128))"));
}
(It would be good to add also a Down() method removing the column.)
Warning: Be careful when running this migration if you already have existing records in the tables with an empty Subscription_Id column value (or if you are adding a new Subscription_Id column to a table that already have records). The empty column will be filled with the value of the Subscription_Id in the connection that is executing the migration, which probably will be wrong (you probably don't want all the existing records to be associated to that specific subscription). In that case you may want to include explicit UPDATE instructions with the right Subscription_Id values in your Up() method, with the Sql() method. Something like this:
Sql("UPDATE SomeEntitiesTable SET Subscription_Id= '19bc9b0d-28dd-4510-bd5e-d6b6d445f511' WHERE Id IN (1, 2, 5)");
With Code First you should also remove the Subscription_Id properties from your model classes. If you can't, at least add explicit Ignore() instructions in your configuration code for the Subscription_Id columns, you don't want them in your EF mappings.
Note: I'm assuming here that you created a RLS policy in your DB that uses UserId parameter in SESSION_CONTEXT, and that your application code is setting that value when opening the DB connection, via a DbConnectionInterceptor or something similar.
This page contains more info.
Entity Framework 6 Casscading Deletes and DropForeignKey fails on auto generated constraint name
I've been running into a bit of an issue with Entity Framework and cascade deletes between two tables on several one-to-many relationships.
Initially it looked like the correct path to take was to configure the table mappings with the OnModelCreating method of DbContext turning off cascade delete in a manner such as
modelBuilder.Entity<SourceTable>()
.HasOptional(x => x.NavigationProperty)
.WithOptionalDependent()
.WillCascadeOnDelete(false);
This however did not work throwing an exception stating
Cannot delete or update a parent row: a foreign key constraint fails...
More research lead me to believe that this is because all affected entities must be loaded into the context (eager fetched) so that entity framework may set the FK references to null as part of the transaction. This is not practical for my needs based on the size of the relational graph I'd be dealing with.
My next approach was to modify the Seed method of the Configuration class and run some arbitrary SQL to drop the Foreign Key constraint and re-add it as a ON DELETE SET NULL constaint. This worked in most cases, however one of the consraints has what appears to be an auto generated unpredicatable name that is diffrent on each call of Update-Database. Given that the name can't be predicted the ALTER statments aren't particualr helpful
context.Database.ExecuteSqlCommand(#"ALTER TABLE SourceTable DROP FOREIGN KEY FK_9405957d032142c3a1227821a9ed1fdf;
ALTER TABLE SourceTable
ADD CONSTRAINT FK_ReasonableName
FOREIGN KEY (NavigationProperty_Id) REFERENCES NavigationProperty (Id) ON DELETE SET NULL;");
Finally, I've taken the apprach to use the migration functionality (DbMigration) and override Up method and leveraging the DropForeignKey method along side more explicit SQL to re-add the constraint (EF does not appear to provide a factility to create a ON DELETE SET NULL constraint).
DropForeignKey("SourceTable", "NavigationProperty_Id", "DestinationTable");
Sql("ALTER TABLE SourceTable ADD CONSTRAINT FK_ReasonableName FOREIGN KEY (NavigationProperty_Id) REFERENCES DestinationTable (Id) ON DELETE SET NULL;");
This works great, up until I encounter the constraint with the auto generate name. At this point the DropForeignKey method fails with an exception that is swallowed up by
System.Runtime.Serialization.SerializationException: Type is not resolved for member 'MySql.Data.MySqlClient.MySqlException,MySql.Data...
When dumping the migration to a SQL script file it becomes clear that the DropForeignKey simply generates a FK with a more predictable, non-ambiguous byte stream array.
Is there a proper EF Code First approach to solve the problem of setting FK column values to null when deleting the refrenced row, or am I stuck having to hand code SQL in order to gain this functionality?
I have a junction table with and idenity primary key columns to realize a many to many relationship. Visual Studio automatically detects it as a many to many relationship and the junction table is not an entity.
How can i realize it that also this table is generated as an entity? I need this for breeze.js .
You just need to add additional columns (or properties) to that table (or model).
You said that your table has acolumn named ID and it's the primary key withe IsIdentity set to true. It must works, I'm using this approach...
There must be a problem or missing with your table definition. However, if all are OK, just add a nullable column in your table and update your model from database. The problem will go away.
In my MS SQL Server 2008 database I have self-referenced table with categories for hierarchy (ID and ParentID). Table have a self Foreign Key constraint and "Instead of Delete" trigger to perform deleting the full node with its children.
To manage data I'm using Entity Framework (4.3), with the model generated from DB with self-tracking entities and ObjectContext (generated by VS template). EDM also have self-referenced association on "category" entity.
I am faced with problem when trying to delete any parent row that has at least one child row.
After I call:
Entity.MarkAsDeleted();
Context.SaveChanges();
In SQL Server Profiler I see that EF first generates an update statement to set ParentID of child row(s) to null and then deletes parent row! Of course cascade rule in DB doesn't work and child nodes remains both in EF context and DB.
I've tried to set association rule "On delete" to "Cascade" and to "None" but it doesn't make sense...
How can I perform a cascade delete in a self-referenced table with EF, or at least how to prevent EF from updating parent IDs of child rows?
PS: here I found exactly the same problem without answer (MSDN)