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- Get Started
- Product
- Resources
- Tools & SDKs
- Framework
- Reference
4.4. Module Link
In this chapter, you’ll learn what a module link is.
What is a Module Link?#
Since modules are isolated, you can't access another module's data models to add a relation to it or extend it.
Instead, you use a module link. A module link forms an association between two data models of different modules, while maintaining module isolation.
How to Define a Module Link?#
1. Create Link File#
Links are defined in a TypeScript or JavaScript file under the src/links
directory. The file defines the link using the defineLink
function imported from @medusajs/framework/utils
and exports it.
For example:
The defineLink
function accepts as parameters the link configurations of each module's data model. A module has a special linkable
property that holds these configurations for its data models.
In this example, you define a module link between the hello
module's MyCustom
data model and the Product Module's Product
data model.
2. Sync Links#
After defining the link, run the db:sync-links
command:
The Medusa application creates a new table for your link to store the IDs of linked records.
Use this command whenever you make changes to your links. For example, run this command if you remove your link definition file.
db:migrate
command, which both runs the migrations and syncs the links.How Module Links Work?#
When you define a module link, the Medusa application creates a table in the database for that link.
Then, when you create links between records of the data models, the IDs of these data models are stored as a new record in the link's table.
When to Use Module Links#
- You want to create a relation between data models from different modules.
- You want to extend the data model of another module.
Define a List Link#
By default, the defined link establishes a one-to-one relation: a record of a data model is linked to one record of the other data model.
To specify that a data model can have multiple of its records linked to the other data model's record, use the isList
option.
For example:
In this case, you pass an object of configuration as a parameter instead. The object accepts the following properties:
linkable
: The data model's link configuration.isList
: Whether multiple records can be linked to one record of the other data model.
In this example, a record of product
can be linked to more than one record of myCustom
.
Set Delete Cascades on Link#
To enable delete cascade on a link so that when a record is deleted, its linked records are also deleted, pass the deleteCascade
property in the object passed to defineLink
.
For example:
In this example, when a product is deleted, its linked myCustom
record is also deleted.