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Postgres on update cascade8/25/2023 ![]() Why would one ever want a query to be refused like that? And "CASCADE" isn't even the only option (besides none) there are multiple other values you can use which cause various behaviour (which I don't understand). I'm basically confused about the entire concept of "ON UPDATE" and "ON DELETE". ![]() In the test2 table, again as I understand it, if the "othertable" either changes the "id" column values, or deletes any record(s), that means that PostgreSQL will refuse to perform the query if there are records in test2 which reference the ones being modified. This seems, on the surface, like what should be the default behaviour. In the test1 table, as I understand it, if the "othertable" either changes the "id" column values, or deletes any record(s), that means that the referenced records in the test1 table will either be updated or deleted. Since this is not done by default, there must be a reason for this! After all, the default behaviour is always (or at least should always be) the most commonly needed behaviour: CREATE TABLE "test2"įOREIGN KEY (referenceid) REFERENCES "othertable" (id) This code goes out of its way to explicitly add the technically "unnecessary" part: "ON UPDATE CASCADE ON DELETE CASCADE". Example: CREATE TABLE "test1"įOREIGN KEY (referenceid) REFERENCES "othertable" (id) ON UPDATE CASCADE ON DELETE CASCADE However, something which has always confused me is whether or not I should be explicitly setting the "ON UPDATE" and "ON DELETE" features (in lack of a better term). Query q = session.createQuery("from Department where departmentId = :departmentId ") ĭepartment department = (Department)q.list().get(0) įor (Subject sdr :department.I understand what foreign keys are, and have made a point of including them wherever they make sense for all my database tables that I design. You need to loop all the ‘subject’ and delete it one by one. If we need to delete the department and all the referenced subjects then we will delete both of them individually when we are not using cascading. It automatically builds the query for the referenced table Subject whenever the Department is saved. Here, we did’nt need to specify the session.save() method for subject separately. Example #1: Cascade save-updateĮxample of adding a department and its subjects into the database.įirstly, we will perform the task of saving both the entities individually without using the cascade property of save-update.Ĭode: Without Cascade Department department = new Department() ĭepartment department = new Department() There is a one-to-many association between departments and subjects. Examples of Cascade in HibernateĬonsider example where we maintain the data of departments and then the subjects under each department. Now, let us see how cascade can be used in hibernate and how it makes it easy to perform operations for related referenced objects without extra coding for them. In both the methods if cascade property is set to all then it means that all the above-mentioned cascade values and operations will be performed. In the case of annotations, annotation can be used to mention all the cascade values inside the braces just after annotation. While using it in the XML files we can use the cascade property or keyword and then assigning the cascade values to it in a comma-separated format. It is necessary to know that cascade property can be used in both configurations using an XML file as well as using annotations in the hibernate framework. ![]() However, we will some of the cascading properties that are most commonly used. Some of the above mentioned cascading values are deprecated nowadays. Types of Cascading Values and Operations Supported by Hibernateĭifferent types of cascading values and operations supported by Hibernate are given below: It is the convenient solution provided which saves the lines of the code needed to be added for handling sate of the other side while doing it manually. By default, there are no operations cascaded to the association. The cascade is defined in the association with the help of the keyword cascade and it specifies all the operations that must be cascaded to the target of the association and mostly used while collection mapping. Web development, programming languages, Software testing & others Start Your Free Software Development Course
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