db\ActiveQueryInterface indexBy()

The name of the column by which the query results should be indexed by. This can also be a callable (e.g. anonymous function) that returns the index value based on the given row or model data. The signature of the callable should be:

// $model is an AR instance when `asArray` is false,
// or an array of column values when `asArray` is true.
function ($model)
{
    // return the index value corresponding to $model
}

The query object itself