code: func (e *executor) executeSetRow(ctx context.Context, index string, c *pql.Call, shards []uint64, opt *execOptions) (bool, error) {
  	// Ensure the field type supports Store().
  	fieldName, err := c.FieldArg()
  	if err != nil {
  		return false, errors.New("field required for Store()")
  	}
  	field := e.Holder.Field(index, fieldName)
  	if field == nil {
  		return false, ErrFieldNotFound
  	}
  	if field.Type() != FieldTypeSet {
  		return false, fmt.Errorf("can't Store() on a %s field", field.Type())
  	}
  
  	// Execute calls in bulk on each remote node and merge.
  	mapFn := func(shard uint64) (interface{}, error) {
  		return e.executeSetRowShard(ctx, index, c, shard)
  	}
  
  	// Merge returned results at coordinating node.
  	reduceFn := func(prev, v interface{}) interface{} {
  		val := v.(bool)
  		if prev == nil {
  			return val
  		}
  		return val || prev.(bool)
  	}
  
  	result, err := e.mapReduce(ctx, index, shards, c, opt, mapFn, reduceFn)
  	return result.(bool), err
  }
docs: // executeSetRow executes a Store() call.