![]() ![]() ![]() The columns must be called A and B where A points to the model that comes first in the alphabet and B points to the model which comes last in the alphabet. A foreign key column that points to Post called B.A foreign key column that points to Category called A.ColumnsĪ relation table for an implicit m-n-relation must have exactly two columns: For example, for a relation named "MyRelation" the corresponding table will be called _MyRelation. This will change the name given to the relation table in the database. When creating an implicit m-n-relation yourself in the Prisma schema file, you can configure the relation to have a different name. In the example, the correct table name is _CategoryToPost. Then the name of the second table in alphabetical order (in this case Post).Then the name of the first table in alphabetical order (in this case Category).If you want a relation table to be picked up by introspection as an implicit m-n-relation, the name must follow this exact structure: The following example assumes you want to create a relation table to get an implicit m-n-relation for two models called Post and Category. If you obtain your data model from introspection, you can still use implicit m-n-relations by following Prisma's conventions for relation tables. You cannot use a in place of an use either of these features, you must use an explicit m-n instead.Ĭonventions for relation tables in implicit m-n relations.Require both models to have a single Be aware that: This is because these take a fixed value for implicit m-n-relations and cannot be changed. If you do use the attribute, you cannot use the references, fields, onUpdate or onDelete arguments. Use a specific convention for relation tablesĭo not require the attribute unless you need to disambiguate relations with a name, e.g. } ) Rules for defining an implicit m-n relation Creates a new Category that is associated with the newly created Post record.Creates a new record in the relation table CategoriesOnPosts.You can query the relation model directly ( prisma.categoriesOnPosts(.)), or use nested queries to go from Post -> CategoriesOnPosts -> Category or the other way. The following section demonstrates how to query an explicit m-n-relation. If you're not using Prisma Migrate but obtain your data model from introspection, you can still make use of implicit m-n-relations by following Prisma's conventions for relation tables. When you don't need to attach additional information to the relation, you can model m-n-relations as implicit m-n-relations. ![]() Note that the same rules as for 1-n relations apply (because Post↔ CategoriesOnPosts and Category ↔ CategoriesOnPosts are both in fact 1-n relations), which means one side of the relation needs to be annotated with the attribute. In this example, the model representing the relation table also defines additional fields that describe the Post/ Category relationship - who assigned the category ( assignedBy), and when the category was assigned ( assignedAt):ĪLTER TABLE "CategoriesOnPosts" ADD CONSTRAINT "CategoriesOnPosts_categoryId_fkey" FOREIGN KEY ( "categoryId" ) REFERENCES "Category" ( "id" ) ON DELETE RESTRICT ON UPDATE CASCADE The relation table CategoriesOnPosts connects related Post and Category records. The fields of a relation table model are both annotated relation fields ( post and category) with a corresponding relation scalar field ( postId and categoryId). One model that represents the relation table, such as CategoriesOnPosts (also sometimes called JOIN, link or pivot table) in the underlying database.Two models with m-n relation, such as Category and Post.Explicit m-n relations define three models: In an explicit m-n relation, the relation table is represented as a model in the Prisma schema and can be used in queries. You can always migrate to an explicit m-n-relation later if needed. We recommend using implicit m-n-relations if you do not need to store any additional meta-data in the relation table itself. m-n-relations can be either explicit or implicit in the Prisma schema. In relational databases, m-n-relations are typically modelled via relation tables. Prisma schema syntax and the implementation in the underlying database differs between relational databases and MongoDB. Many-to-many (m-n) relations refer to relations where zero or more records on one side of the relation can be connected to zero or more records on the other side. ![]()
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