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fetch.go
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fetch.go
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// Copyright (c) 2013 Couchbase, Inc.
// Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
// except in compliance with the License. You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
// Unless required by applicable law or agreed to in writing, software distributed under the
// License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
// either express or implied. See the License for the specific language governing permissions
// and limitations under the License.
package xpipeline
import (
"github.com/couchbaselabs/clog"
"github.com/couchbaselabs/dparval"
"github.com/couchbaselabs/tuqtng/ast"
"github.com/couchbaselabs/tuqtng/catalog"
"github.com/couchbaselabs/tuqtng/misc"
"github.com/couchbaselabs/tuqtng/network"
"github.com/couchbaselabs/tuqtng/query"
)
const FETCH_BATCH_SIZE = 1000
type Fetch struct {
Base *BaseOperator
bucket catalog.Bucket
batch dparval.ValueCollection
projection ast.Expression
as string
ids []string
rowsFetched int
}
func NewFetch(bucket catalog.Bucket, projection ast.Expression, as string) *Fetch {
return &Fetch{
Base: NewBaseOperator(),
bucket: bucket,
batch: make(dparval.ValueCollection, 0, FETCH_BATCH_SIZE),
projection: projection,
as: as,
}
}
func (this *Fetch) SetSource(source Operator) {
this.Base.SetSource(source)
}
func (this *Fetch) SetIds(ids []string) {
this.ids = ids
}
func (this *Fetch) GetChannels() (dparval.ValueChannel, PipelineSupportChannel) {
return this.Base.GetChannels()
}
func (this *Fetch) Run(stopChannel misc.StopChannel) {
clog.To(CHANNEL, "fetch operator starting")
if this.Base.Source != nil {
this.Base.RunOperator(this, stopChannel)
} else {
defer close(this.Base.itemChannel)
defer close(this.Base.supportChannel)
defer close(this.Base.upstreamStopChannel)
for _, id := range this.ids {
doc := dparval.NewValue(map[string]interface{}{})
doc.SetAttachment("meta", map[string]interface{}{"id": id})
this.processItem(doc)
}
this.afterItems()
}
clog.To(CHANNEL, "fetch operator finished, fetched %d", this.rowsFetched)
}
func (this *Fetch) processItem(item *dparval.Value) bool {
// add this item to the batch
this.batch = append(this.batch, item)
// if the batch is full, do a fetch
if len(this.batch) >= FETCH_BATCH_SIZE {
return this.flushBatch()
}
return true
}
func (this *Fetch) afterItems() {
// source may have closed with a parital batch
this.flushBatch()
}
func (this *Fetch) flushBatch() bool {
defer func() {
// no matter what hapens in this function
// clear out the batch and start a new one
this.batch = make(dparval.ValueCollection, 0, FETCH_BATCH_SIZE)
}()
// gather the ids
ids := make([]string, 0, FETCH_BATCH_SIZE)
for _, v := range this.batch {
meta := v.GetAttachment("meta")
if meta != nil {
id, ok := meta.(map[string]interface{})["id"]
if !ok {
return this.Base.SendError(query.NewError(nil, "asked to fetch an item without a key"))
} else {
ids = append(ids, id.(string)) //FIXME assert ids always strings
}
} else {
return this.Base.SendError(query.NewError(nil, "asked to fetch an item without a meta"))
}
}
// now do a bulk fetch
bulkResponse, err := this.bucket.BulkFetch(ids)
if err != nil {
return this.Base.SendError(query.NewError(err, "error getting bulk response"))
}
// now we need to emit the bulk fetched items in the correct order (from the id list)
for _, v := range ids {
item, ok := bulkResponse[v]
if ok {
if this.projection != nil {
projectedVal, err := this.Base.projectedValueOfResultExpression(item, ast.NewResultExpression(this.projection))
if err != nil {
switch err := err.(type) {
case *dparval.Undefined:
// undefined contributes nothing to the result map
continue
default:
return this.Base.SendError(query.NewError(err, "unexpected error projecting fetch expression"))
}
} else {
if this.as != "" {
this.Base.SendItem(dparval.NewValue(map[string]interface{}{this.as: projectedVal}))
} else {
this.Base.SendItem(projectedVal)
}
}
} else {
if this.as != "" {
this.Base.SendItem(dparval.NewValue(map[string]interface{}{this.as: item}))
} else {
this.Base.SendItem(item)
}
}
this.rowsFetched += 1
}
}
return true
}
func (this *Fetch) SetQuery(q network.Query) {
this.Base.SetQuery(q)
}