コード例 #1
0
ファイル: datastore_query.go プロジェクト: nishanths/gae
// GetBinaryBounds gets the binary encoding of the upper and lower bounds of
// the inequality filter on fq, if any is defined. If a bound does not exist,
// it is nil.
//
// NOTE: if fq specifies a descending sort order for the inequality, the bounds
// will be inverted, incremented, and flipped.
func GetBinaryBounds(fq *ds.FinalizedQuery) (lower, upper []byte) {
	// Pick up the start/end range from the inequalities, if any.
	//
	// start and end in the reducedQuery are normalized so that `start >=
	// X < end`. Because of that, we need to tweak the inequality filters
	// contained in the query if they use the > or <= operators.
	if ineqProp := fq.IneqFilterProp(); ineqProp != "" {
		_, startOp, startV := fq.IneqFilterLow()
		if startOp != "" {
			lower = serialize.ToBytes(startV)
			if startOp == ">" {
				lower = increment(lower)
			}
		}

		_, endOp, endV := fq.IneqFilterHigh()
		if endOp != "" {
			upper = serialize.ToBytes(endV)
			if endOp == "<=" {
				upper = increment(upper)
			}
		}

		// The inequality is specified in natural (ascending) order in the query's
		// Filter syntax, but the order information may indicate to use a descending
		// index column for it. If that's the case, then we must invert, swap and
		// increment the inequality endpoints.
		//
		// Invert so that the desired numbers are represented correctly in the index.
		// Swap so that our iterators still go from >= start to < end.
		// Increment so that >= and < get correctly bounded (since the iterator is
		// still using natrual bytes ordering)
		if fq.Orders()[0].Descending {
			hi, lo := []byte(nil), []byte(nil)
			if len(lower) > 0 {
				lo = increment(serialize.Invert(lower))
			}
			if len(upper) > 0 {
				hi = increment(serialize.Invert(upper))
			}
			upper, lower = lo, hi
		}
	}
	return
}