Relationships that point to multiple records are displayed in the frontend in the Related Data and Explorer sections.
One-to-Many relations
In a one-to-many relationship, one record from a collection is connected to multiple records in another.
Think about countries and towns: a country has multiple towns, and each town belongs to a country.
// Link 'countries' to 'towns'agent.customizeCollection('countries', collection =>collection.addOneToManyRelation('myTowns','towns', { originKey:'country_id', originKeyTarget:'id',// Optional (uses primary key of countries by default) }););
Many-to-Many relations
In a many-to-many relation, three collections are used instead of two to build the relation.
This allows multiple records from one collection to be connected to multiple records from another.
For instance, on a movie recommendation website, each user can rate many movies, and each movie can be rated by many users. The three collections which are being used are users (the "origin" collection), ratings (the "through" collection), and movies (the "foreign" collection).
// Create one side of the relation ...agent.customizeCollection('users', collection => {collection.addManyToManyRelation('ratedMovies','movies','ratings', { originKey:'user_id', foreignKey:'movie_id', });});// ... and the other oneagent.customizeCollection('movies', collection => {collection.addManyToManyRelation('whoRatedThisMovie','users','ratings', { originKeyTarget:'id',// Optional (uses primary key of movies by default) originKey:'movie_id', foreignKey:'user_id', foreignKeyTarget:'id',// Optional (uses primary key of users by default) });});
External relations
External relations allow defining collection which will only be available through the "Related Data" section or a given model.
Note that external relations do not support pagination.
conststates= [ { code:'AK', name:'Alaska', zipMin:99501, zipMax:99950, closeTo: [] }, { code:'AL', name:'Alabama', zipMin:35004, zipMax:36925, closeTo: ['TE','MI','GE','FL'] }, { code:'AR', name:'Arkansas', zipMin:71601, zipMax:72959, closeTo: ['OK','TX','LO','MI'] }, { code:'AZ', name:'Arizona', zipMin:85001, zipMax:86556, closeTo: ['NM','CO','UT','NE'] }, { code:'CA', name:'California', zipMin:90001, zipMax:96162, closeTo: ['OR','NE','AZ'] },// ....];agent.customizeCollection('address', collection => {collection.addExternalRelation('nearStates', {// Define schema of the records in the relation. schema: { code:'Number', name:'String' },// Which fields are needed from the parent record to run the handler?// Dependencies are optional: by default only the primary key of address would be provided dependencies: ['country','zipCode'],// Compute list of records from the parent recordlistRecords:async ({ country, zipCode }) => {if (country ==='USA') {conststate=states.find(s =>s.zipMin < zipCode && zipCode <s.zipMax);returnstates.filter(s =>state.closeTo.includes(s.code)); }return []; }, });});