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resolver.go
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resolver.go
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// Way to resolve database references without DBRefs.
// Can only work in the same database for now.
//
// Now only resolves one level.
// Later the package will be able to handle cascading reference resolution.
// Will detect circular references, so it won't run into an infinite loop.
//
// It will resolve any value in the seed, at any depth which is a bson.ObjectId or []bson.ObjectId, and has a key of the form:
// _collectionName or optionally _collectionName_fieldName (if there are more than one references in to the same collection)
package resolver
import (
"fmt"
"labix.org/v2/mgo"
"labix.org/v2/mgo/bson"
"strings"
)
type Mapper struct {
Map *map[string]interface{}
Key string
Ids []bson.ObjectId
Single bool
}
func hasObjId(sl []interface{}) bool {
for _, v := range sl {
_, ok := v.(bson.ObjectId)
if ok {
return true
}
}
return false
}
// Returns a []bson.ObjectId from a []interface{}.
// Non ObjectId values are appended as empty ObjectIds (they are not valid).
func toIdSlice(from []interface{}) []bson.ObjectId {
ret := []bson.ObjectId{}
for _, v := range from {
val, ok := v.(bson.ObjectId)
if ok {
ret = append(ret, val)
} else {
ret = append(ret, "")
}
}
return ret
}
// Separates each Mapper in accum by the collection they belong to.
func separateByColl(accum []Mapper) map[string][]Mapper {
ret := map[string][]Mapper{}
for _, v := range accum {
if string(v.Key[0]) == "_" {
collname := strings.Split(v.Key, "_")[1]
_, has := ret[collname]
if !has {
ret[collname] = []Mapper{}
}
ret[collname] = append(ret[collname], v)
}
}
return ret
}
// Recursively traverses the whole input and extracts all ObjectIds from it (remembering their position) to further processing.
// Caution: bson.M s are intentionally not handled here.
func extractIds(dat interface{}, acc *[]Mapper, parent map[string]interface{}, key string) {
switch val := dat.(type) {
case []interface{}:
// if hasObjId(slice)... // This is a yet not handled corner case.
for _, v := range val {
mapval, ok := v.(map[string]interface{})
if !ok {
continue
}
extractIds(v, acc, mapval, "")
}
case map[string]interface{}:
for i, v := range val {
if i == "_id" {
continue
}
if slice, is_slice := v.([]interface{}); is_slice && hasObjId(slice) && string(i[0]) == "_" {
m := Mapper{Map: &val, Key: i, Ids: toIdSlice(slice)}
*acc = append(*acc, m)
} else {
extractIds(v, acc, val, i)
}
}
case bson.ObjectId:
if string(key[0]) == "_" {
m := Mapper{Map: &parent, Key: key, Ids: []bson.ObjectId{val}, Single: true}
*acc = append(*acc, m)
}
case bson.M:
panic("Please convert all bson.M maps to map[string]interface{} in query results.")
}
}
type m map[string]interface{}
// Returns all ids from a []Mapper, so they can be queried.
func collectIds(ms []Mapper) []bson.ObjectId {
ret := []bson.ObjectId{}
for _, v := range ms {
for _, z := range v.Ids {
if z != "" {
ret = append(ret, z) // Added to support []interface{}s where not all members are bson.ObjectIds.
}
}
}
return ret
}
// Takes a doc (z) from a query and with the help of the index it replaces the ObjectID with the doc.
func burnItIn(z bson.M, acc []Mapper, ind map[string][][2]int) {
str_id := z["_id"].(bson.ObjectId).Hex()
if index_sl, has := ind[str_id]; has {
for _, v := range index_sl {
mapper := acc[v[0]]
if mapper.Single {
(*mapper.Map)[mapper.Key] = z
} else {
(*mapper.Map)[mapper.Key].([]interface{})[v[1]] = z
}
}
} else {
panic("Unkown bug in resolver.")
}
}
func query(db *mgo.Database, collname string, ids []bson.ObjectId, keys map[string]interface{}) []interface{} {
var res []interface{}
q := db.C(collname).Find(m{"_id": m{"$in": ids}})
if keys != nil {
q.Select(keys)
}
err := q.All(&res)
if err != nil {
panic(err)
}
return res
}
// Glues everything together.
func queryAndSet(db *mgo.Database, acc []Mapper, keys map[string]interface{}) {
ind := index(acc)
sep_accs := separateByColl(acc)
for i, v := range sep_accs {
ids := collectIds(v) // TODO
res := query(db, i, ids, keys) // TODO: It's inefficient ATM, we should only collect and query the ids belonging to the given collection, not all of them.
for _, z := range res {
burnItIn(z.(bson.M), acc, ind)
}
}
}
// Index creates an index out of a []Mapper.
// Index key will be the string representation of the bson.ObjectId.
// The value will be the [position in accum][position in ObjectId slice of the Mapper instance]
func index(accum []Mapper) map[string][][2]int {
ret := map[string][][2]int{}
for i, v := range accum {
for j, z := range v.Ids {
if z == "" { // Added to support []interface{}s where not all members are bson.ObjectIds.
continue
}
hexid := z.Hex()
_, has := ret[hexid]
if !has {
ret[hexid] = [][2]int{}
}
ret[hexid] = append(ret[hexid], [2]int{i, j})
}
}
return ret
}
func ResolveOne(db *mgo.Database, seed interface{}, keys map[string]interface{}) error {
return ResolveAll(db, []interface{}{seed}, keys)
}
func ResolveAll(db *mgo.Database, seeds []interface{}, keys map[string]interface{}) (err error) {
defer func() {
if r := recover(); r != nil {
err = fmt.Errorf(fmt.Sprint(r))
}
}()
acc := &[]Mapper{}
for _, v := range seeds {
extractIds(v, acc, v.(map[string]interface{}), "")
}
queryAndSet(db, *acc, keys)
return nil
}