I need to change the primary key (#Id) of an entity from natural key to a new field that represents a surrogate key (it will use #GeneratedValue(strategy=GenerationType.AUTO)).
What is the easiest way to update the database schema other than dropping the table and letting Hibernate to create it again?
I was trying to let Hibernate update the schema automagically with hibernate.hbm2ddl.auto set to update, but it didn't work out. I suppose that Hibernate autoupdate doesn't support such drastic changes of database schemas.
If it were only one entity, I'd
make the changes in the database manually (SQL)
and update the Hibernate mapping accordingly
Related
The SQL Server 2016 system versioning is cool. I am using the free Developer version. Thanks MS!
I am unable to figure out if it will give me versioning of many to many relationships. I have a User object that has a collection of Roles and vice versa. Entity Framework has generated the UserRoles table that holds the relationship between User and Roles. I was able to turn on system versioning for the User and Roles tables using this article http://sqlhints.com/tag/modify-existing-table-as-system-versioned-temporal-table/.
But, I am not able to turn on for UserRoles. I get an error
Setting SYSTEM_VERSIONING to ON failed because table has a FOREIGN KEY with cascading DELETE or UPDATE.
Does this mean we cannot know the versioning for many-many relationships?
For eg.
on 6/1 - User1 had role1 and role2, but
on 6/4 - User1's role changed to role1 and role3
So, if I wanted to know the state of the user on 6/1, I thought that's possible only by turning on system versioning on UserRoles, but that's not working.
Is this doable or not supported by SQL Server 2016? If not, is there any other way this can be accomplished?
It's important to notice that the limitation of using CASCADE on FOREIGN KEY constraints in temporal tables is applicable only to SQL Server 2016. In SQL Server 2017, this limitation doesn't exist anymore.
This is the relevant part from the official documentation:
ON DELETE CASCADE and ON UPDATE CASCADE are not permitted on the
current table. In other words, when temporal table is referencing
table in the foreign key relationship (corresponding to
parent_object_id in sys.foreign_keys) CASCADE options are not allowed.
To work around this limitation, use application logic or after
triggers to maintain consistency on delete in primary key table
(corresponding to referenced_object_id in sys.foreign_keys). If
primary key table is temporal and referencing table is non-temporal,
there's no such limitation.
> NOTE: This limitation applies to SQL Server 2016 only. CASCADE options
are supported in SQL Database and SQL Server 2017 starting from CTP
2.0.
Sounds like it's the ON UPDATE CASCADE or ON UPDATE DELETE foreign key that's the issue. Remove the cascading and replace that with a delete proc that knows and handles the proper relationships and you should be fine.
Personally, I like knowing what my deletes/updates are doing rather than trusting the relationships to handle all of them. I can see potential locking issues as well as know that there are times I really want to prevent an update or delete rather than letting it cascade through all of the tables unseen.
ON DELETE CASCADE and ON UPDATE CASCADE are not permitted on the current table. In other words, when temporal table is referencing table in the foreign key relationship (corresponding to parent_object_id in sys.foreign_keys) CASCADE options are not allowed. To work around this limitation, use application logic or after triggers to maintain consistency on delete in primary key table (corresponding to referenced_object_id in sys.foreign_keys). If primary key table is temporal and referencing table is non-temporal, there’s no such limitation.
I have two tables in two different databases. In table1 (in database1) there is a column called column1 and it is a primary key. Now in table2 (in database2) there is a column called column2 and I want to add it as a foreign key.
I tried to add it and it gave me the following error:
Msg 1763, Level 16, State 0, Line 1
Cross-database foreign key references are not supported. Foreign key Database2.table2.
Msg 1750, Level 16, State 0, Line 1
Could not create constraint. See previous errors.
How do I do that since the tables are in different databases.
You would need to manage the referential constraint across databases using a Trigger.
Basically you create an insert, update trigger to verify the existence of the Key in the Primary key table. If the key does not exist then revert the insert or update and then handle the exception.
Example:
Create Trigger dbo.MyTableTrigger ON dbo.MyTable, After Insert, Update
As
Begin
If NOT Exists(select PK from OtherDB.dbo.TableName where PK in (Select FK from inserted) BEGIN
-- Handle the Referential Error Here
END
END
Edited: Just to clarify. This is not the best approach with enforcing referential integrity. Ideally you would want both tables in the same db but if that is not possible. Then the above is a potential work around for you.
If you need rock solid integrity, have both tables in one database, and use an FK constraint. If your parent table is in another database, nothing prevents anyone from restoring that parent database from an old backup, and then you have orphans.
This is why FK between databases is not supported.
You could use check constraint with a user defined function to make the check. It is more reliable than a trigger. It can be disabled and reenabled when necessary same as foreign keys and rechecked after a database2 restore.
CREATE FUNCTION dbo.fn_db2_schema2_tb_A
(#column1 INT)
RETURNS BIT
AS
BEGIN
DECLARE #exists bit = 0
IF EXISTS (
SELECT TOP 1 1 FROM DB2.SCHEMA2.tb_A
WHERE COLUMN_KEY_1 = #COLUMN1
) BEGIN
SET #exists = 1
END;
RETURN #exists
END
GO
ALTER TABLE db1.schema1.tb_S
ADD CONSTRAINT CHK_S_key_col1_in_db2_schema2_tb_A
CHECK(dbo.fn_db2_schema2_tb_A(key_col1) = 1)
In my experience, the best way to handle this when the primary authoritative source of information for two tables which are related has to be in two separate databases is to sync a copy of the table from the primary location to the secondary location (using T-SQL or SSIS with appropriate error checking - you cannot truncate and repopulate a table while it has a foreign key reference, so there are a few ways to skin the cat on the table updating).
Then add a traditional FK relationship in the second location to the table which is effectively a read-only copy.
You can use a trigger or scheduled job in the primary location to keep the copy updated.
The short answer is that SQL Server (as of SQL 2008) does not support cross database foreign keys--as the error message states.
While you cannot have declarative referential integrity (the FK), you can reach the same goal using triggers. It's a bit less reliable, because the logic you write may have bugs, but it will get you there just the same.
See the SQL docs # http://msdn.microsoft.com/en-us/library/aa258254%28v=sql.80%29.aspx Which state:
Triggers are often used for enforcing
business rules and data integrity. SQL
Server provides declarative
referential integrity (DRI) through
the table creation statements (ALTER
TABLE and CREATE TABLE); however, DRI
does not provide cross-database
referential integrity. To enforce
referential integrity (rules about the
relationships between the primary and
foreign keys of tables), use primary
and foreign key constraints (the
PRIMARY KEY and FOREIGN KEY keywords
of ALTER TABLE and CREATE TABLE). If
constraints exist on the trigger
table, they are checked after the
INSTEAD OF trigger execution and prior
to the AFTER trigger execution. If the
constraints are violated, the INSTEAD
OF trigger actions are rolled back and
the AFTER trigger is not executed
(fired).
There is also an OK discussion over at SQLTeam - http://www.sqlteam.com/forums/topic.asp?TOPIC_ID=31135
Achieving referential integrity accross databases is not an easy task.
Here is a list of frequently employed mechanisms:
Clone & Sync: The referenced data is regularly cloned/merged into the referencing database. This may be suitable if the referenced data is rarely changing. You end up with two physical copies of the same data, and need a reliable process to keep them in sync (e.g. with an ETL pipeline).
Triggers: Changes to the referencing data and the referenced data are caught by SQL triggers, which ensure referential integrity. However, triggers can be slow, and may not fire at a database restore. It cannot hurt to run scheduled consistency checks as part of the operations monitoring. Write access to the referenced database is required for installing and maintaining the trigger.
Check constraints: SQL-Server offers user-defined contraints, which ensure that every row satisfies a given condition. One can exploit this functionality by writing a user defined function that checks the existence of a row in the referenced data, and then use this function as a CHECK's predicate in the referencing table. This does not catch changes in the referenced data. It is an RDBMS-specific solution, but works accross server boundaries (e.g. using linked servers). It is a good choice for referencing globally unique IDs, such as article codes in a company's ERP system, which never get deleted or re-assigned.
Re-think database architecture: When all the above mechanisms are unsatisfactory, multiple databases may be merged in a single database. The originating database names can become schema names, allowing effective grouping of database objects.
As the error message says, this is not supported on sql server.
The only way to ensure refrerential integrity is to work with triggers.
We moved our DB from an instance of SQL 2005 to a new SQL 2008r2 server. We changed the connection strings in our app to point to new database, even modified the ProviderManifestToken from 2005 to 2008. Everything was working fine until we tried to add entities from our database to our existing edmx model. I'm using the 'update model from database' wizard to add tables to the edmx diagram. The tables will appear in the diagram but only some have their associations and/or foreign keys imported. If I switch the connection string to point back to the old 2005 sql instance everything imports correctly and associations are present. I'm happy to provide additional details if necessary. I can't find a pattern to this at all. What gives?
Update: I created a new project, added an edmx, pointed it to the 2008r2 db instance, selected tables that I know have associations but the designer failed to pick up the associations. Is there something I need to install on the SQL server to get EF to work?
It's working for now. Deleting the connection string from the web.config and then using 'Update Model from Database' and going through the 'Add new connection' dialog to point to the database on the new server seemed to make it behave. If this stops working I'll post back.
Update: Turns out I had two problems. The second was that one of the tables in our DB had two nearly identical redundant indexes on the same column; a clustered PK index and a unique, non-clustered index. So any time I created a foreign key pointing to this table the database chose the unique non-clustered index to enforce the constraint (why? I don't know). But Entity Framework didn't like it and would not create or even recognize the foreign key association. I had to delete the extra non-clustered index and re-create all the foreign keys so they would point to the clustered index. Once that was done I updated my model from the database and all associations were present.
Here's the SQL query I used to check which indexes my foreign keys were using:
SELECT *
FROM INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS C
ORDER BY CONSTRAINT_NAME
The UNIQUE_CONSTRAINT_NAME column for the FK in question should point to a clustered PK for it to work.
How did you move the database to the 2008 Server? Sounds like some or all of the relationships/constraints were not migrated. That would explain why the associations are not showing up when you point to the 2008 database.
I have two tables in two different databases. In table1 (in database1) there is a column called column1 and it is a primary key. Now in table2 (in database2) there is a column called column2 and I want to add it as a foreign key.
I tried to add it and it gave me the following error:
Msg 1763, Level 16, State 0, Line 1
Cross-database foreign key references are not supported. Foreign key Database2.table2.
Msg 1750, Level 16, State 0, Line 1
Could not create constraint. See previous errors.
How do I do that since the tables are in different databases.
You would need to manage the referential constraint across databases using a Trigger.
Basically you create an insert, update trigger to verify the existence of the Key in the Primary key table. If the key does not exist then revert the insert or update and then handle the exception.
Example:
Create Trigger dbo.MyTableTrigger ON dbo.MyTable, After Insert, Update
As
Begin
If NOT Exists(select PK from OtherDB.dbo.TableName where PK in (Select FK from inserted) BEGIN
-- Handle the Referential Error Here
END
END
Edited: Just to clarify. This is not the best approach with enforcing referential integrity. Ideally you would want both tables in the same db but if that is not possible. Then the above is a potential work around for you.
If you need rock solid integrity, have both tables in one database, and use an FK constraint. If your parent table is in another database, nothing prevents anyone from restoring that parent database from an old backup, and then you have orphans.
This is why FK between databases is not supported.
You could use check constraint with a user defined function to make the check. It is more reliable than a trigger. It can be disabled and reenabled when necessary same as foreign keys and rechecked after a database2 restore.
CREATE FUNCTION dbo.fn_db2_schema2_tb_A
(#column1 INT)
RETURNS BIT
AS
BEGIN
DECLARE #exists bit = 0
IF EXISTS (
SELECT TOP 1 1 FROM DB2.SCHEMA2.tb_A
WHERE COLUMN_KEY_1 = #COLUMN1
) BEGIN
SET #exists = 1
END;
RETURN #exists
END
GO
ALTER TABLE db1.schema1.tb_S
ADD CONSTRAINT CHK_S_key_col1_in_db2_schema2_tb_A
CHECK(dbo.fn_db2_schema2_tb_A(key_col1) = 1)
In my experience, the best way to handle this when the primary authoritative source of information for two tables which are related has to be in two separate databases is to sync a copy of the table from the primary location to the secondary location (using T-SQL or SSIS with appropriate error checking - you cannot truncate and repopulate a table while it has a foreign key reference, so there are a few ways to skin the cat on the table updating).
Then add a traditional FK relationship in the second location to the table which is effectively a read-only copy.
You can use a trigger or scheduled job in the primary location to keep the copy updated.
The short answer is that SQL Server (as of SQL 2008) does not support cross database foreign keys--as the error message states.
While you cannot have declarative referential integrity (the FK), you can reach the same goal using triggers. It's a bit less reliable, because the logic you write may have bugs, but it will get you there just the same.
See the SQL docs # http://msdn.microsoft.com/en-us/library/aa258254%28v=sql.80%29.aspx Which state:
Triggers are often used for enforcing
business rules and data integrity. SQL
Server provides declarative
referential integrity (DRI) through
the table creation statements (ALTER
TABLE and CREATE TABLE); however, DRI
does not provide cross-database
referential integrity. To enforce
referential integrity (rules about the
relationships between the primary and
foreign keys of tables), use primary
and foreign key constraints (the
PRIMARY KEY and FOREIGN KEY keywords
of ALTER TABLE and CREATE TABLE). If
constraints exist on the trigger
table, they are checked after the
INSTEAD OF trigger execution and prior
to the AFTER trigger execution. If the
constraints are violated, the INSTEAD
OF trigger actions are rolled back and
the AFTER trigger is not executed
(fired).
There is also an OK discussion over at SQLTeam - http://www.sqlteam.com/forums/topic.asp?TOPIC_ID=31135
Achieving referential integrity accross databases is not an easy task.
Here is a list of frequently employed mechanisms:
Clone & Sync: The referenced data is regularly cloned/merged into the referencing database. This may be suitable if the referenced data is rarely changing. You end up with two physical copies of the same data, and need a reliable process to keep them in sync (e.g. with an ETL pipeline).
Triggers: Changes to the referencing data and the referenced data are caught by SQL triggers, which ensure referential integrity. However, triggers can be slow, and may not fire at a database restore. It cannot hurt to run scheduled consistency checks as part of the operations monitoring. Write access to the referenced database is required for installing and maintaining the trigger.
Check constraints: SQL-Server offers user-defined contraints, which ensure that every row satisfies a given condition. One can exploit this functionality by writing a user defined function that checks the existence of a row in the referenced data, and then use this function as a CHECK's predicate in the referencing table. This does not catch changes in the referenced data. It is an RDBMS-specific solution, but works accross server boundaries (e.g. using linked servers). It is a good choice for referencing globally unique IDs, such as article codes in a company's ERP system, which never get deleted or re-assigned.
Re-think database architecture: When all the above mechanisms are unsatisfactory, multiple databases may be merged in a single database. The originating database names can become schema names, allowing effective grouping of database objects.
As the error message says, this is not supported on sql server.
The only way to ensure refrerential integrity is to work with triggers.
I am building my mapping and then using schema export to update my DB. However, if I delete an association in my mapping, since it's no longer in the mapping, when I run SchemaExport, it will not delete the foreign key for the deleted association. This means that it then fails to drop the table associated with that foreign key. Which further means that it can't recreate the table and I get a "There is already an object named Foo in the database" exception. Is there any way to brute delete the table via Schema Export?
The cleanest way is to do SchemaExport.Drop with the old nhibernate configuration, then create with the new one.
Alternatively you could drop and recreate the database itself, here's an example which does this at file level for SQL Server Express: http://nicholas.piasecki.name/blog/2010/01/integration-testing-with-sql-server-express-2008-nhibernate-and-mstest/