我正在使用OpenStreeMap数据转储到MongoDB实例中，以下集合存在nodes，ways和relations。
我正在查询给定地理空间点的半径范围内的所有节点，并了解这些节点之间的关系我正在使用ways集合尝试检索包含我之前地理空间中任何节点的所有方法查询。
然后，我试图在way文档中包含地理空间坐标（它已经有loc.coordinates字段，由于某种原因是空的），使用它在字段中包含的节点ID { {1}}。除this answer中提供的帮助外，我还得到了以下代码：
loc.nodes但最后的管道没有任何回报。
package main
import (
"fmt"
mgo "gopkg.in/mgo.v2"
"gopkg.in/mgo.v2/bson"
)
// GeoJSON Holds data of geospatial points
type GeoJSON struct {
Type string `json:"-"`
Coordinates []float64 `json:"coordinates"`
}
type waynodes struct {
Type string
Coordinates []float64
Nodes []int
}
// OSMNode Represet a single point in space.
// https://wiki.openstreetmap.org/wiki/Node
//
// A node is one of the core elements in the OpenStreetMap data model. It
// consists of a single point in space defined by its latitude, longitude and
// node id. A third, optional dimension (altitude) can also be included:
// key:ele (abrev. for "elevation"). A node can also be defined as part of a
// particular layer=* or level=*, where distinct features pass over or under
// one another; say, at a bridge. Nodes can be used to define standalone point
// features, but are more often used to define the shape or "path" of a way.
type OSMNode struct {
ID int `bson:"_id"`
Location GeoJSON `bson:"loc"`
Tags map[string]interface{} `bson:"tags,omitempty"`
}
// OSMWay Represent an ordered list of nodes
// https://wiki.openstreetmap.org/wiki/Way
//
// A way is an ordered list of nodes which normally also has at least one tag
// or is included within a Relation. A way can have between 2 and 2,000 nodes,
// although it's possible that faulty ways with zero or a single node exist. A
// way can be open or closed. A closed way is one whose last node on the way is
// also the first on that way. A closed way may be interpreted either as a
// closed polyline, or an area, or both.
//
// The nodes defining the geometry of the way are enumerated in the correct
// order, and indicated only by reference using their unique identifier. These
// nodes must have been already defined separately with their coordinates.
type OSMWay struct {
ID int `bson:"_id"`
Location waynodes `bson:"loc"`
Tags map[string]interface{}
}
// km2miles convert a distance in kilometers to miles and then return the
// radius of such distance.
func km2miles(dist float64) float64 {
r := dist * 0.621371
// https://en.wikipedia.org/wiki/Earth_radius#Fixed_radius
return r / 3963.2
}
// nodes2list return a string list of node IDs from a list of OSMNode objects
func nodes2list(l []OSMNode) []int {
var list []int
for _, v := range l {
list = append(list, v.ID)
}
return list
}
// GetGeoWithinPos Return all points in a given point of Earth within the
// radius of `dist`.
func (db *DB) GetGeoWithinPos(long, lat, dist float64) ([]OSMWay, error) {
// Look at `nodes` document in our `osm` database
c := db.m.DB("osm").C("nodes")
// Query all nodes within a range from a spatial point: It should be
// equivalent to:
// db.nodes.find(
// {loc:
// {$geoWithin:
// {$centerSphere: [[-83.4995983, 10.1033002], 0.186411 / 3963.2]
// }
// }
// }, {"_id": 1});
var nodesresult []OSMNode
err := c.Find(bson.M{
"loc": bson.M{
"$geoWithin": bson.M{
"$centerSphere": []interface{}{
[]interface{}{long, lat}, km2miles(dist),
},
},
},
}).Select(bson.M{"_id": 1}).All(&nodesresult)
if err != nil {
return nil, err
} else if nodesresult == nil {
return nil, fmt.Errorf("Nodes not found on %f lat, %f long in a radius of %f km", lat, long, dist)
} else if nodesresult[0].ID == 0 {
return nil, fmt.Errorf("Nodes incorrectly unmarshall: %#v", nodesresult[0:3])
}
// Prepare a pipeline
pipe := []bson.M{
{
// Match only ways that contains the ID of the nodes
// from the query on `qsn`
"$match": bson.M{
"loc.nodes": bson.M{
"$in": nodes2list(nodesresult), // Return []int
},
},
},
{
// Now look for the nodes at `nodes` collection present
// at `loc.nodes` field...
"$lookup": bson.M{
"from": "nodes",
"localField": "loc.nodes",
"foreignField": "_id",
"as": "loc.coordinates",
},
},
{
// ...and set the field `loc.coordinates` with the
// coordinates of all nodes.
"$addField": bson.M{
"loc.coordinates": bson.M{
"$reduce": bson.M{
"input": "$loc.coordinates.loc.coordinates",
"initialValue": []float64{},
"in": bson.M{"$concatArrays": []string{"$$this", "$$value"}},
},
},
},
},
}
// Query ways collection
w := db.m.DB("osm").C("ways")
var ways []OSMWay
// Execute the pipeline
err = w.Pipe(pipe).All(&ways)
if ways == nil {
return nil, fmt.Errorf("Ways not found within %0.2f km/radius (%f mil/radius)", dist, km2miles(dist))
}
return ways, err
}
我想知道我在这里做错了什么，为什么mgo不能做我想做的事。
为了完整起见，这里是测试定义：
$ go test
--- FAIL: TestFetchData (1.80s)
db_test.go:16: from -83.4995983long, 10.1033002lat: Ways not found within 1.00 km/radius (0.000157 mil/radius)
这是func TestFetchData(t *testing.T) {
db, err := NewDBConn("", "", "localhost", 27017)
if err != nil {
t.Fatalf("Could not establish connection with MongoDB: %s", err)
}
// Get data from some location in my hometown
_, err := db.GetGeoWithinPos(-83.4995983, 10.1033002, 1.0)
if err != nil {
t.Fatalf("from -83.4995983long, 10.1033002lat: %s", err)
}
}
集合中的示例文档：
ways这是来自{
"_id":492464922,
"tags":{
"maxspeed":"20",
"surface":"asphalt",
"highway":"residential",
"oneway":"yes",
"name":"Avenida 1"
},
"loc":{
"type":"Polygon",
"coordinates":[
],
"nodes":[
445848963,
4844871065,
432568566
]
}
}
集合的示例文档：
nodes这将是我想要返回的示例输出我正在尝试传递给管道：
{
"_id":445848963,
"loc":{
"type":"Point",
"coordinates":[
-83.5047254,
10.0984515
]
}
}
答案 0 :(得分：1)
这是因为汇总管道中存在拼写错误。该运算符名为$addFields而非$addField（缺少s）。
w.Pipe()的方法调用应该引发Unrecognized pipeline stage name: '$addField'行的错误。但是，您的代码未检查err返回的Pipe()变量。由于您只检查由于错误而为零的变量ways，因此您的方法返回(nil, "Ways not found within %0.2f km/radius (%f mil/radius)");从而屏蔽了管道错误。
我建议先检查内容检查err：
err = w.Pipe(pipe).All(&ways)
if err != nil {
//handle error
}