Population.md

Population

There are no joins in RxDB but sometimes we still want references to documents in other collections. This is where population comes in. You can specify a relation to another RxDocument in the same or another RxCollection of the same database.

Schema with ref

The ref-keyword describes which collection the field-value belongs to.

export const refHuman = {
    title: 'human related to other human',
    version: 0,
    properties: {
        name: {
            primary: true,
            type: 'string'
        },
        bestFriend: {
            ref: 'human',     // refers to collection human
            type: 'string'    // ref-values must always be string (primary of foreign RxDocument)
        }
    }
};

populate()

via method

To get the refered RxDocument, you can use the populate()-method. It takes the field-path as attribute and returns a Promise which resolves to the foreign document or null if not found.

const doc = await humansCollection.findOne().exec();
const bestFriend = await doc.populate('bestFriend');

via getter

You can also get the populated RxDocument with the direct getter. Therefore you have to add the underscore _ to the fieldname. This works also on nested values.

const doc = await humansCollection.findOne().exec();
const bestFriend = await doc.bestFriend_; // added underscore_

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If you are new to RxDB, you should continue here