objection-qb-distinctOn.js

class BaseQueryBuilder extends objection.QueryBuilder {
  distinctOn (columns, tableStar = `${this.modelClass().tableName}.*`) {
    columns = asArray(columns)

    const identifiers = columns.map(() => '??').join(', ')

    columns = columns.map(column => {
      return column.split('.').length === 1
        ? `${this.modelClass().tableName}.${column}`
        : column
    })

    const distinctOn = raw(`DISTINCT ON (${identifiers}) ??`, [
      ...columns,
      tableStar
    ])

    return this.select(distinctOn)
  }
}