Computed foreign keys
You may want to create a relationship between 2 Collections, but you don't have a foreign key that is ready to use to connect them.
This is done with the following steps:
- create a new Field containing a foreign key,
- create a relation using it.
We have 2 Collections:
Customers
and Messages
, linked together by a one-to-many
relationship.We want to create a
ManyToOne
relationship with the last message sent by a given customer.agent.customizeCollection('customers', collection => {
// Create foreign key
collection.addField('lastMessageId', {
columnType: 'Number',
dependencies: ['id'],
getValues: async (customers, context) => {
// We're using Forest Admin's Query Interface (you can use an ORM or plain SQL)
const messages = context.dataSource.getCollection('messages');
const conditionTree = {
field: 'customer_id',
operator: 'In',
value: customers.map(c => c.id),
};
const rows = await messages.aggregate(
{ conditionTree },
{ operation: 'Max', field: 'id', groups: [{ field: 'customer_id' }] },
);
return customers.map(record => {
return rows.find(row => row.group.customer_id === record.id)?.value ?? null;
});
},
});
// Implement the 'In' operator.
collection.replaceFieldOperator(
'lastMessageId',
'In',
async (lastMessageIds, context) => {
const records = await context.dataSource
.getCollection('messages')
.list(
{ conditionTree: { field: 'id', operator: 'In', value: lastMessageIds } },
['customer_id'],
);
return { field: 'id', operator: 'In', value: records.map(r => r.customer_id) };
},
);
// Create relationships using the foreign key we just added.
collection.addManyToOneRelation('lastMessage', 'messages', {
foreignKey: 'lastMessageId',
});
});
You have 2 Collections and both contain users: one comes from your database, and the other one is connected to the CRM that your company uses.
There is no common id between them that can be used to tell Forest Admin how to link them together, however, both Collections have
firstName
, lastName
, and birthDate
fields, which taken together, are unique enough.agent
.customizeCollection('databaseUsers', createFilterableIdentityField)
.customizeCollection('crmUsers', createFilterableIdentityField)
.customizeCollection('databaseUsers', createRelationship)
.customizeCollection('crmUsers', createInverseRelationship);
/**
* Concatenate firstname, lastname and birthData to make a unique identifier
* and ensure that the new field is filterable
*/
function createFilterableIdentityField(collection) {
// Create foreign key on the collection from the database
collection.addField('userIdentifier', {
columnType: 'String',
dependencies: ['firstName', 'lastName', 'birthDate'],
getValues: user => user.map(u => `${u.firstName}/${u.lastName}/${u.birthDate}`),
});
// Implement 'In' filtering operator (required)
collection.replaceFieldOperator('userIdentifier', 'In', values => ({
aggregator: 'Or',
conditions: values.map(value => ({
aggregator: 'And',
conditions: [
{ field: 'firstName', operator: 'Equal', value: value.split('/')[0] },
{ field: 'lastName', operator: 'Equal', value: value.split('/')[1] },
{ field: 'birthDate', operator: 'Equal', value: value.split('/')[2] },
],
})),
}));
}
/** Create relationship between databaseUsers and crmUsers */
function createRelationship(databaseUsers) {
databaseUsers.addOneToOneRelation('userFromCrm', 'crmUsers', {
originKey: 'userIdentifier',
originKeyTarget: 'userIdentifier',
});
}
/** Create relationship between crmUsers and databaseUsers */
function createInverseRelationship(crmUsers) {
crmUsers.addManyToOneRelation('userFromDatabase', 'databaseUsers', {
foreignKey: 'userIdentifier',
foreignKeyTarget: 'userIdentifier',
});
}
Last modified 1mo ago