Golang FinalizedQuery.Project方法代码示例

func pickQueryStrategy(fq *ds.FinalizedQuery, rq *reducedQuery, cb ds.RawRunCB, head *memStore) queryStrategy {
	if fq.KeysOnly() {
		return &keysOnlyStrategy{cb, stringset.New(0)}
	}
	if len(fq.Project()) > 0 {
		return newProjectionStrategy(fq, rq, cb)
	}
	return newNormalStrategy(rq.aid, rq.ns, cb, head)
}

func countQuery(fq *ds.FinalizedQuery, aid, ns string, isTxn bool, idx, head *memStore) (ret int64, err error) {
	if len(fq.Project()) == 0 && !fq.KeysOnly() {
		fq, err = fq.Original().KeysOnly(true).Finalize()
		if err != nil {
			return
		}
	}
	err = executeQuery(fq, aid, ns, isTxn, idx, head, func(_ *ds.Key, _ ds.PropertyMap, _ ds.CursorCB) error {
		ret++
		return nil
	})
	return
}

func (d *dsTxnBuf) Count(fq *ds.FinalizedQuery) (count int64, err error) {
	// Unfortunately there's no fast-path here. We literally have to run the
	// query and count. Fortunately we can optimize to count keys if it's not
	// a projection query. This will save on bandwidth a bit.
	if len(fq.Project()) == 0 && !fq.KeysOnly() {
		fq, err = fq.Original().KeysOnly(true).Finalize()
		if err != nil {
			return
		}
	}
	err = d.Run(fq, func(_ *ds.Key, _ ds.PropertyMap, _ ds.CursorCB) error {
		count++
		return nil
	})
	return
}

// adjustQuery applies various mutations to the query to make it suitable for
// merging. In general, this removes limits and offsets the 'distinct' modifier,
// and it ensures that if there are sort orders which won't appear in the
// result data that the query is transformed into a projection query which
// contains all of the data. A non-projection query will never be transformed
// in this way.
func adjustQuery(fq *ds.FinalizedQuery) (*ds.FinalizedQuery, error) {
	q := fq.Original()

	// The limit and offset must be done in-memory because otherwise we may
	// request too few entities from the underlying store if many matching
	// entities have been deleted in the buffered transaction.
	q = q.Limit(-1)
	q = q.Offset(-1)

	// distinction must be done in-memory, because otherwise there's no way
	// to merge in the effect of the in-flight changes (because there's no way
	// to push back to the datastore "yeah, I know you told me that the (1, 2)
	// result came from `/Bob,1`, but would you mind pretending that it didn't
	// and tell me next the one instead?
	q = q.Distinct(false)

	// since we need to merge results, we must have all order-related fields
	// in each result. The only time we wouldn't have all the data available would
	// be for a keys-only or projection query. To fix this, we convert all
	// Projection and KeysOnly queries to project on /all/ Orders.
	//
	// FinalizedQuery already guarantees that all projected fields show up in
	// the Orders, but the projected fields could be a subset of the orders.
	//
	// Additionally on a keys-only query, any orders other than __key__ require
	// conversion of this query to a projection query including those orders in
	// order to merge the results correctly.
	//
	// In both cases, the resulting objects returned to the higher layers of the
	// stack will only include the information requested by the user; keys-only
	// queries will discard all PropertyMap data, and projection queries will
	// discard any field data that the user didn't ask for.
	orders := fq.Orders()
	if len(fq.Project()) > 0 || (fq.KeysOnly() && len(orders) > 1) {
		q = q.KeysOnly(false)

		for _, o := range orders {
			if o.Property == "__key__" {
				continue
			}
			q = q.Project(o.Property)
		}
	}

	return q.Finalize()
}

func (d *dsTxnBuf) Run(fq *ds.FinalizedQuery, cb ds.RawRunCB) error {
	if start, end := fq.Bounds(); start != nil || end != nil {
		return errors.New("txnBuf filter does not support query cursors")
	}

	limit, limitSet := fq.Limit()
	offset, _ := fq.Offset()
	keysOnly := fq.KeysOnly()

	project := fq.Project()

	bufDS, parentDS, sizes := func() (ds.RawInterface, ds.RawInterface, *sizeTracker) {
		if !d.haveLock {
			d.state.Lock()
			defer d.state.Unlock()
		}
		return d.state.bufDS, d.state.parentDS, d.state.entState.dup()
	}()

	return runMergedQueries(fq, sizes, bufDS, parentDS, func(key *ds.Key, data ds.PropertyMap) error {
		if offset > 0 {
			offset--
			return nil
		}
		if limitSet {
			if limit == 0 {
				return ds.Stop
			}
			limit--
		}
		if keysOnly {
			data = nil
		} else if len(project) > 0 {
			newData := make(ds.PropertyMap, len(project))
			for _, p := range project {
				newData[p] = data[p]
			}
			data = newData
		}
		return cb(key, data, nil)
	})
}

func newProjectionStrategy(fq *ds.FinalizedQuery, rq *reducedQuery, cb ds.RawRunCB) queryStrategy {
	proj := fq.Project()

	projectionLookups := make([]projectionLookup, len(proj))
	for i, prop := range proj {
		projectionLookups[i].propertyName = prop
		lookupErr := fmt.Errorf("planning a strategy for an unfulfillable query?")
		for j, col := range rq.suffixFormat {
			if col.Property == prop {
				projectionLookups[i].suffixIndex = j
				lookupErr = nil
				break
			}
		}
		impossible(lookupErr)
	}
	ret := &projectionStrategy{cb: cb, project: projectionLookups}
	if fq.Distinct() {
		ret.distinct = stringset.New(0)
	}
	return ret
}

func (d rdsImpl) fixQuery(fq *ds.FinalizedQuery) (*datastore.Query, error) {
	ret := datastore.NewQuery(fq.Kind())

	start, end := fq.Bounds()
	if start != nil {
		ret = ret.Start(start.(datastore.Cursor))
	}
	if end != nil {
		ret = ret.End(end.(datastore.Cursor))
	}

	for prop, vals := range fq.EqFilters() {
		if prop == "__ancestor__" {
			p, err := dsF2RProp(d.aeCtx, vals[0])
			if err != nil {
				return nil, err
			}
			ret = ret.Ancestor(p.Value.(*datastore.Key))
		} else {
			filt := prop + "="
			for _, v := range vals {
				p, err := dsF2RProp(d.aeCtx, v)
				if err != nil {
					return nil, err
				}

				ret = ret.Filter(filt, p.Value)
			}
		}
	}

	if lnam, lop, lprop := fq.IneqFilterLow(); lnam != "" {
		p, err := dsF2RProp(d.aeCtx, lprop)
		if err != nil {
			return nil, err
		}
		ret = ret.Filter(lnam+" "+lop, p.Value)
	}

	if hnam, hop, hprop := fq.IneqFilterHigh(); hnam != "" {
		p, err := dsF2RProp(d.aeCtx, hprop)
		if err != nil {
			return nil, err
		}
		ret = ret.Filter(hnam+" "+hop, p.Value)
	}

	if fq.EventuallyConsistent() {
		ret = ret.EventualConsistency()
	}

	if fq.KeysOnly() {
		ret = ret.KeysOnly()
	}

	if lim, ok := fq.Limit(); ok {
		ret = ret.Limit(int(lim))
	}

	if off, ok := fq.Offset(); ok {
		ret = ret.Offset(int(off))
	}

	for _, o := range fq.Orders() {
		ret = ret.Order(o.String())
	}

	ret = ret.Project(fq.Project()...)
	if fq.Distinct() {
		ret = ret.Distinct()
	}

	return ret, nil
}

// runMergedQueries executes a user query `fq` against the parent datastore as
// well as the in-memory datastore, calling `cb` with the merged result set.
//
// It's expected that the caller of this function will apply limit and offset
// if the query contains those restrictions. This may convert the query to
// an expanded projection query with more data than the user asked for. It's the
// caller's responsibility to prune away the extra data.
//
// See also `dsTxnBuf.Run()`.
func runMergedQueries(fq *ds.FinalizedQuery, sizes *sizeTracker,
	memDS, parentDS ds.RawInterface, cb func(k *ds.Key, data ds.PropertyMap) error) error {

	toRun, err := adjustQuery(fq)
	if err != nil {
		return err
	}

	cmpLower, cmpUpper := memory.GetBinaryBounds(fq)
	cmpOrder := fq.Orders()
	cmpFn := func(i *item) string {
		return i.getCmpRow(cmpLower, cmpUpper, cmpOrder)
	}

	dedup := stringset.Set(nil)
	distinct := stringset.Set(nil)
	distinctOrder := []ds.IndexColumn(nil)
	if len(fq.Project()) > 0 { // the original query was a projection query
		if fq.Distinct() {
			// it was a distinct projection query, so we need to dedup by distinct
			// options.
			distinct = stringset.New(0)
			proj := fq.Project()
			distinctOrder = make([]ds.IndexColumn, len(proj))
			for i, p := range proj {
				distinctOrder[i].Property = p
			}
		}
	} else {
		// the original was a normal or keys-only query, so we need to dedup by keys.
		dedup = stringset.New(0)
	}

	stopChan := make(chan struct{})

	parIter := queryToIter(stopChan, toRun, parentDS)
	memIter := queryToIter(stopChan, toRun, memDS)

	parItemGet := func() (*item, error) {
		for {
			itm, err := parIter()
			if itm == nil || err != nil {
				return nil, err
			}
			encKey := itm.getEncKey()
			if sizes.has(encKey) || (dedup != nil && dedup.Has(encKey)) {
				continue
			}
			return itm, nil
		}
	}
	memItemGet := func() (*item, error) {
		for {
			itm, err := memIter()
			if itm == nil || err != nil {
				return nil, err
			}
			if dedup != nil && dedup.Has(itm.getEncKey()) {
				continue
			}
			return itm, nil
		}
	}

	defer func() {
		close(stopChan)
		parItemGet()
		memItemGet()
	}()

	pitm, err := parItemGet()
	if err != nil {
		return err
	}

	mitm, err := memItemGet()
	if err != nil {
		return err
	}

	for {
		// the err can be set during the loop below. If we come around the bend and
		// it's set, then we need to return it. We don't check it immediately
		// because it's set after we already have a good result to return to the
		// user.
		if err != nil {
			return err
		}

		usePitm := pitm != nil
		if pitm != nil && mitm != nil {
//.........这里部分代码省略.........