I have 2 tables, 1 main table, 1 junction table and 1 lookup table. It's a 1-to-many-to-1 relationship. I'm looking for a way to delete all the entries from the junction table only, without removing the lookup value.
An example of my tables are below
Record table
id
name
Junction table
recordid
lookupid
Lookups table
lookupid
lookupname
Currently I'm passing in an updated model and I'm trying to delete all the junction records before reading the new chosen values. So far everything I've tried deletes out the record from the lookup table as well.
foreach (var lookup in recordFromDB.Lookups.ToList()) {
_context.Lookups.Remove(DesignSoftware);
}
Try this - just using the .Clear() method on the navigation property should remove any navigation (a.k.a. "junction") entries - but not the actual Lookups entries:
recordFromDB.Lookups.Clear();
YourContext.SaveChanges();
Related
I have 2 tables. First table is called Person. Second table is called PersonRule. Person table has much columns. But PersonRule has just 2 columns. In the person table, there is a column called ruleid. The column at the same time, there is in the PersonRule table. Is it possible, when i insert to data Person table, i want to automatically create a record in PersonRule table without trigger.?
And in PostgreSQL how can i do this.?
Using Postgres database. I have an existing table, and several existing Views that query that table.
Call the table, 'contacts'.
I alter the table, changing the name to 'contacts_backup'. I then created a new table with the same name the older table used to have 'contacts'
Now it appears that if I query the existing views, the data is still retrieved from the renamed table, contacts_backup, and not the new table, 'contacts'.
Can this be? How can I update the Views to query the new table of the same name, and not the renamed contacts_backup?
My new table is actually a foreign table, but shouldn't the principle be the same? I was expecting the existing tables to query against the new table, not the old renamed one.
What is an efficient way to update the existing views to query from the new table?
This is because PostgreSQL does not store the view definition as an SQL string, but as a parsed query tree.
These parsed query trees don't contain the names of the referenced objects, but only their object identifier (oid), which does not change when you rename an object.
The same is true for table columns. This all holds for foreign tables as well.
When you examine the view definition, for example with pg_get_viewdef, the parse tree is rendered as text, so you will see the changed names.
If you want to change the table that a view is referring to, the only solution is to either DROP the view and CREATE it again, or you can use CREATE OR REPLACE VIEW.
I have table location in postgres database with more then 50.000.000+ rows, and i decide to do partition!
Table parent have columns id,place and i want to do partition onplace column, with php and mysql i get all distinct places(about 300) and foreach
CREATE TABLE child_place_name (CHECK (place=place_name))INHERITS(location)
and after that in each child table
INSERT INTO child_place_name SELECT * FROM location WHERE place=place_name
and that works perfectly!
After i delete rows from parent class with
DELETE FROM location WHERE tableoid=('location'::regclass)::oid;
i that affected all rows is table!
Then i try to do query and a get times and realize that now is time for query 3 or more times longer then before.
I also have problem that my affect on speed: first i can't set primary key on id column in child tables, but i set index key on place(also index is set on place column in parent table), and also i can't set unique key on id and place columns i got error multiple parameters in not allowed(or something like that)
All i want is select side of table i don't need rules or triggers to set when i insert in parent table,cause that is another problem,only i want to know what is wrong with this approach!Maybe 300+ tables is to much?
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.
I was trying to insert values from one table to another from two different databases.
My issue is I have two tables with a relation and the first table is having an identity column also.
eg table first(id, Name) - table second(id, address)
So now both the table exist with values in a db and i am trying to copy values from this db to another db.
So when I insert values from first db to second db the the first table will insert values for the Id column by itself so now I have to link that id to the second table.
How can I do that?
UPDATE using MSSQL server 2000
You can use #scope_identity immediately after your insert in SQL server 2000 which will give you the last id within the current scope but I'm not sure how that would work with bulk inserting of data
http://msdn.microsoft.com/en-us/library/ms190315.aspx
If this were SQL Server 2005 or later I would suggest using the output clause in your insert statement to retrieve the ids just inserted, but that was not available in SQL Server 2000.
If your data contains some column or series of columns which is unique other than the identity column, then you can query your first table based on that series of columns to get the ids and use that to populate your second table.
If the target tables were empty you could use SET IDENTITY_INSERT ON - this would allow to insert original values to identity columns, and you will not have to update referenced IDs. Of course if there is any existing ids that can overlap inserted ids - that is not the solution.
If names in first tables are unique, you could boild mapping between new and old ids and perform update something like this:
UPDATE S
SET S.id = F.id
FROM second S
INNER JOIN first_original FO ON FO.id = S.id
INNER JOIN first F ON F.name = FO.name
If names are not unique, then original ids should be saved in "first" in order to provide mapping between old and new ids. It can be temporary new column that can be deleted after ids in "second" will be updated.
Or as Rich Andrews said you could use #scope_identity, but in this case you will have to perform insert one by one - declare a cursor on source table, insert each record, get its new id and insert it into "second" table.