I have a database table 'MyTable' that has a trigger upon update of field 'Status' in it.
Below is a dummy-code of what i'm trying to do:
MyTable table = new Mytable();
table.setTableId(1);
table.setStatus ("NEW");
em.persist (table); //At this point the trigger did not kick in since this inserted a new record
...
MyTable table2 = em.find(MyTable.class, 1);
table2.setStatus ("NEW");
em.merge(table2)//Even though im updating the record with the same status with the same value, i still want the trigger to kick. However the trigger is not being activated.
...
MyTable table3 = em.find(MyTable.class, 1);
table3.setStatus ("OLD");
em.merge(table3)//The trigger is being activated here since the status is different the status value when it was inserted the first time.
Long story short, how can i make the changes done to 'transfer2' to trigger an update even though the status is the same?
-Thanks
Use em.flush(); to synchronize the persistence context to the underlying database. Your pending queries shall be send to database, but you still can have a complete rollback.
JPA does not update object that have no changes.
You could try changing to something else (flush), then changing it back.
You could also use a JPQL update query to update it.
Depending on your JPA provider you could probably force it to update fields that have not changed, but this would lead to very bad performance.
Could you please try updating the enity and commit the transaction, without using merge.
Like
em.getTransaction().begin();
MyTable table2 = em.find(MyTable.class, 1);
table2.setStatus ("NEW");
//em.merge(table2)//Even though im updating the record with the same status with the
// same value, i still want the trigger to kick. However the trigger is not being activated.
em.getTransaction().commit();
Related
My android device calls an endpoint in spring boot. When two devices call in parallel - the insert is not completed for the first call, the second call reaches the db meanwhile. The first call seems to be generating the primary key and the second call sees the conflict and hence tries to update. The first call is supposed to insert, subsequent calls should increment the value by 1. The insert is not completed so the second call tries to update the value. Hence it updates the value as null. Subsequent calls do value + 1 hence they update null again. How do I handle this scenario to make sure one call locks the row or how do I solve this problem?
insert
into
table1 (primary_key,
quantity)
values(:primary_key,
:qty) on
conflict primary_key do
update
set
quantity = (
select
coalesce(quantity, 1) + :qty
from
table1
where
primary_key = :primary_key)
where
primary_key = :primary_key;
Note - :qty will be 1 and :primary_key will be the key passed on from the code.
Make your database insert action a transaction (what is a database transaction?), in short it either finishes everything or nothing.
You didn't post your back-end code but for reference it can be done in spring boot like this https://spring.io/guides/gs/managing-transactions/
The explanation is that your subquery doesn't find a row yet, because it is not yet visible to the transaction. Hence the result is NULL.
Avoid that race condition with the much simpler
INSERT INTO table1 (primary_key, quantity)
VALUES (:primary_key, :qty)
ON CONFLICT (primary_key)
DO UPDATE
SET quantity = coalesce(table1.quantity, 1) + EXCLUDED.quantity;
I'm trying to understand how to lock a row, and only release that lock later.
I have a table like this :
create table testTable (Name varchar(100));
Some test data
insert into testTable (name) select 'Bob';
insert into testTable (name) select 'John';
insert into testTable (name) select 'Steve';
Now, I want to select one of those rows, and prevent other other queries from seeing this row. I achieve that like this :
begin transaction;
select * from testTable where name = 'Bob' for update;
In another window, I do this :
select * from testTable for update skip locked;
Great, I don't see 'Bob' in that result set. Now, I want to do something with the primary retrieved row (Bob), and after I did my work, I want to release that row again. Simple answer would be to do :
commit transaction
However, I am running multiple transactions on the same connection, so I can't just begin and commit transactions all over the show. Ideally I would like to have a "named" transaction, something like :
begin transaction 'myTransaction';
select * from testTable where name = 'Bob' for update;
//do stuff with the data, outside sql then later call ...
commit transaction 'myTransaction';
But postgres doesn't support that. I have found "prepare transaction", but that seems to be a pear-shaped path I don't want to go down, especially as these transaction seem to persist through restarts even.
Is there anyway I can have a reference to commit/rollback for a specific transaction?
You can have only one transaction in a database session, so the question as such is moot.
But I assume that you do not really want to run a transaction, you want to block access to a certain row for a while.
It is usually not a good idea to use regular database locks for such a purpose (the exception are advisory locks, which serve exactly that purpose, but are not tied to table rows). The problem is that long database transactions keep autovacuum from doing its job.
I recommend that you add a status column to the table and change the status rather than locking the row. That would server the same purpose in a more natural fashion and make your problem go away.
If you are concerned that the status flag might not get cleared due to application logic problems, replace it with a visible_from column of type timestamp with time zone that initially contains -infinity. Instead of locking the row, set the value to current_timestamp + INTERVAL '5 minutes'. Only select rows that fulfill WHERE visible_from < current_timestamp. That way the “lock” will automatically expire after 5 minutes.
So I am working on adding a last updated time to the database for my app's server. The idea is that it will record the time an update is applied to one of our trips and then the app can send a get request to figure out if it's got all of the correct up to date information.
I've added the column to our table, and provided the service for it all, and finally manage to get a trigger going to update the column every time a change is made to a trip in it's trip table. My problem now comes from the fact that the information that pertains to a trip is stored across a multitude of other tables as well (for instance, there are tables for the routes that make up a trip and the photos that a user can see on the trip, etc...) and if any of that data changes, then the trip's update time also needs to change. I can't for the life of me figure out how to set up the trigger so that when I change some route information, the last updated time for the trip(s) the route belongs to will be updated in it's table.
This is my trigger code as it stands now: it updates the trip table's last updated column when that trip's row is updated.
CREATE OR REPLACE FUNCTION record_update_time() RETURNS TRIGGER AS
$$
BEGIN
NEW.last_updated=now();
RETURN NEW;
END;
$$
LANGUAGE PLPGSQL;
CREATE TRIGGER update_entry_on_entry_change
BEFORE UPDATE ON mydatabase.trip FOR EACH ROW
EXECUTE PROCEDURE record_update_time();
--I used the next two queries just to test that the trigger works. It
--probably doesn't make a difference to you but I'll keep it here for reference
UPDATE mydatabase.trip
SET title='Sample New Title'
WHERE id = 2;
SELECT *
FROM mydatabase.trip
WHERE mydatabase.trip.id < 5;
Now I need it to update when the rows referencing the trip row with a foreign key get updated. Any ideas from someone more experienced with SQL triggers than I?
"mydatabase" is a remarkably unfortunate name for a schema.
The trigger function could look like this:
CREATE OR REPLACE FUNCTION trg_upaft_upd_trip()
RETURNS trigger
LANGUAGE plpgsql AS
$func$
BEGIN
UPDATE mydatabase.trip t -- "mydatabase" = schema name (?!)
SET last_updated = now()
WHERE t.id = NEW.trip_id -- guessing column names
RETURN NULL; -- calling this AFTER UPDATE
END
$func$;
And needs to be used in a trigger on every related table (not on trip itself):
CREATE TRIGGER upaft_upd_trip
AFTER UPDATE ON mydatabase.trip_detail
FOR EACH ROW EXECUTE PROCEDURE trg_upaft_upd_trip();
You also need to cover INSERT and DELETE (and possibly COPY) on all sub-tables ...
This approach has many potential points of failure. As alternative, consider a query or view that computes the latest last_updated from sub-tables dynamically. If you update often this might be the superior approach.
If you rarely UPDATE and SELECT often, your first approach might pay.
I have a Products table which contains an attribute that will get updated via an ERP update by an end user. When that happens I need the update to be replicated in another table. I am not at all experienced with creating T-SQL triggers but I believe it will accomplish my objective.
Example:
In the IC_Products table:
Productkey = 456
StockLocation = ‘GA-07-A250’
In the IC_ProductCustomFields table (will start out the same because I will run a script to make it so):
Productkey = 456
CustomFieldKey = 13
Value = ‘GA-07-A250’
When the IC_Products.StockLocation column gets updated then I want the value in new IC_ProductCustomFields.Value to also get updated automatically and immediately.
If a new record is created in IC_Products then I want a new record to also be created in IC_ProductCustomFields.
I would like to know how to write the trigger script as well as how to implement it. I am using SQL Server 2005.
You want something like this:
CREATE TRIGGER [dbo].[tr_Products_SyncCustomFields] ON [dbo].[IC_Products]
FOR INSERT, UPDATE
AS
-- First, we'll handle the update. If the record doesn't exist, we'll handle that second
UPDATE IC_ProductCustomFields
SET Value = inserted.StockLocation
FROM IC_ProductCustomFields cf
INNER JOIN inserted -- Yes, we want inserted. In triggers you just get inserted and deleted
ON cf.Productkey = inserted.Productkey AND CustomFieldKey = 13;
-- Now handle the insert where required. Note the NOT EXISTS criteria
INSERT INTO IC_ProductCustomFields (Productkey, CustomFieldKey, Value)
SELECT Productkey, CustomFieldKey, Value
FROM inserted
WHERE NOT EXISTS
(
SELECT *
FROM IC_ProductCustomFields
WHERE Productkey = inserted.Productkey AND CustomFieldKey = 13
);
GO
You could, I think, do separate triggers for insert and update, but this will also have the side-effect of restoring your (supposed?) invariants if the custom fields ever get out of sync; even in an update, if the custom field doesn't exist, this will insert the new record as required to bring it back into compliance with your spec.
I have a table in my SQL Server 2008 R2 database, and would like to add a column called LastUpdated, that will automatically be changed every time the row is updated. That way, I can see when each individual row was last updated.
It seems that SQL Server 2008 R2 doesn't have a data type to handle this like earlier versions did, so I'm not sure of the best way to do it. I wondered about using a trigger, but what would happen when the trigger updated the row? Will that fire the trigger again, etc?
To know which row was last updated, you need to create a new column of type DATETIME/DATETIME2 and update it with a trigger. There is no data type that automatically updates itself with date/time information every time the row is updated.
To avoid recursion you can use the UPDATE() clause inside the trigger, e.g.
ALTER TRIGGER dbo.SetLastUpdatedBusiness
ON dbo.Businesses
AFTER UPDATE -- not insert!
AS
BEGIN
IF NOT UPDATE(LastUpdated)
BEGIN
UPDATE t
SET t.LastUpdated = CURRENT_TIMESTAMP -- not dbo.LastUpdated!
FROM dbo.Businesses AS t -- not b!
INNER JOIN inserted AS i
ON t.ID = i.ID;
END
END
GO
In modern versions you can trick SQL Server into doing this using temporal tables:
Maintaining LastModified Without Triggers
But this is full of caveats and limitations and was really only making light of multiple other similar posts:
A System-Maintained LastModifiedDate Column
Tracking Row Changes With Temporal
Columns
How to add “created” and “updated” timestamps without triggers
Need a datetime column that automatically updates
It's not that easy, unfortunately.
You can add a new DATETIME (or DATETIME2) field to your table, and you can give it a default constraint of GETDATE() - that will set the value when a new row is inserted.
Unfortunately, other than creating an AFTER UPDATE trigger, there is no "out of the box" way to keep it updated all the time. The trigger per se isn't hard to write, but you'll have to write it for each and every single table that should have that feature.....