so I have a table A which has a column expiry date. When this date is passed I have to call a API and add new data to table. What is way to do this
things i have thought of are
Database trigger: The problem is trigger can be set only on update, insert.
Creating a separate service which checks expiry, call api and add new data, this problem is expiry_date is just for some seconds, so if this api is slow i will not be able to show latest data.
The main problem i feel with both of solutions is db will receive lots of queries, so i wanted to know if there is other way?
Related
When implementing a system which creates tasks that need to be resolved by some workers, my idea would be to create a table which would have some task definition along with a status, e.g. for document review we'd have something like reviewId, documentId, reviewerId, reviewTime.
When documents are uploaded to the system we'd just store the documentId along with a generated reviewId and leave the reviewerId and reviewTime empty. When next reviewer comes along and starts the review we'd just set his id and current time to mark the job as "in progress" (I deliberately skip the case where the reviewer takes a long time, or dies during the review).
When implementing such a use case in e.g. PostgreSQL we could use the UPDATE review SET reviewerId = :reviewerId, reviewTime: reviewTime WHERE reviewId = (SELECT reviewId from review WHERE reviewId is null AND reviewTime is null FOR UPDATE SKIP LOCKED LIMIT 1) RETURNING reviewId, documentId, reviewerId, reviewTime (so basically update the first non-taken row, using SKIP LOCKED to skip any already in-processing rows).
But when moving from native solution to JDBC and beyond, I'm having troubles implementing this:
Spring Data JPA and Spring Data JDBC don't allow the #Modifying query to return anything else than void/boolean/int and force us to perform 2 queries in a single transaction - one for the first pending row, and second one with the update
one alternative would be to use a stored procedure but I really hate the idea of storing such logic so away from the code
other alternative would be to use a persistent queue and skip the database all along but this introduced additional infrastructure components that need to be maintained and learned. Any suggestions are welcome though.
Am I missing something? Is it possible to have it all or do we have to settle for multiple queries or stored procedures?
Why Spring Data doesn't support returning entity for modifying queries?
Because it seems like a rather special thing to do and Spring Data JDBC tries to focus on the essential stuff.
Is it possible to have it all or do we have to settle for multiple queries or stored procedures?
It is certainly possible to do this.
You can implement a custom method using an injected JdbcTemplate.
I want to "reset" certain data in my database tables using a RESTful method but I'm not sure which one I should be using. UPDATE because I'm deleting records and updating the record where the ID is referenced (but never removing the record where ID lives itself), or DELETE because my main action is to delete associated records and updating is tracking those changes?
I suppose this action can be ran multiple times but the result will be the same, however the ID will always be found when "resetting".
I think you want the DELETE method
I am using FromCache() method whenever I need to retrieve data from the SQL database. There will be a lot of unique queries executed in a single method since it is getting data based on userID. The data associated with the userID will be updated through a separate process which will also trigger an event in the method that controls retrieving. When the data for a specific user is updated, I want to expire the cache for that user so that the next query on that userID will get the most recent data.
I see that EF plus has the option to ExpireTag. Would it be feasible to create a single tag for each userID and then use that to expire the cache?
Would it be feasible to create a single tag for each userID and then use that to expire the cache?
Yes, tag can be used similarly as if you use a cache key.
The best is probably using 2 tags:
Users
[UniqueUserId]
The Users tag will expire all cache related to "users"
The [UniqueUserId] tag will expire all caches related to this specific users
I've created a new trigger(before insert, before update) for a custom object which is going to take the information from a Standard Object (Opportunity) this is the problem that i'm facing..
I'm pulling information from the the Opportunity object (lookup field to User) to the new record in the custom object to trigger email alerts when this custom record is created... (i can't use formulas here) with this method everything is going to work when the custom record is created after that all the information is populated on the Opportunity.. the Problem is that sometimes the fields that i'm getting from the Opportunity are not populated before the custom record is created... how can i run the trigger for the custom object when updating the Opportunity record ?? i'm fairly new to APEX so i will like to get some input on how to get this implemented.. ! Thanks
Could you tell us more about what your algorithm is supposed to do?
As long as I can give you one piece of advice on the use of triggers: if the trigger has to perform actions on the object to which it is assigned, then use these events - before insert, before update. But if the trigger has to perform actions on other objects, then use events - after insert, after update, after delete.
More about triggers:
Force.com Apex Code Developer's Guide
Apex Triggers the Definitive Guide
The repository in the CommonDomain only exposes the "GetById()". So what to do if my Handler needs a list of Customers for example?
On face value of your question, if you needed to perform operations on multiple aggregates, you would just provide the ID's of each aggregate in your command (which the client would obtain from the query side), then you get each aggregate from the repository.
However, looking at one of your comments in response to another answer I see what you are actually referring to is set based validation.
This very question has raised quite a lot debate about how to do this, and Greg Young has written an blog post on it.
The classic question is 'how do I check that the username hasn't already been used when processing my 'CreateUserCommand'. I believe the suggested approach is to assume that the client has already done this check by asking the query side before issuing the command. When the user aggregate is created the UserCreatedEvent will be raised and handled by the query side. Here, the insert query will fail (either because of a check or unique constraint in the DB), and a compensating command would be issued, which would delete the newly created aggregate and perhaps email the user telling them the username is already taken.
The main point is, you assume that the client has done the check. I know this is approach is difficult to grasp at first - but it's the nature of eventual consistency.
Also you might want to read this other question which is similar, and contains some wise words from Udi Dahan.
In the classic event sourcing model, queries like get all customers would be carried out by a separate query handler which listens to all events in the domain and builds a query model to satisfy the relevant questions.
If you need to query customers by last name, for instance, you could listen to all customer created and customer name change events and just update one table of last-name to customer-id pairs. You could hold other information relevant to the UI that is showing the data, or you could simply hold IDs and go to the repository for the relevant customers in order to work further with them.
You don't need list of customers in your handler. Each aggregate MUST be processed in its own transaction. If you want to show this list to user - just build appropriate view.
Your command needs to contain the id of the aggregate root it should operate on.
This id will be looked up by the client sending the command using a view in your readmodel. This view will be populated with data from the events that your AR emits.