英文:
How can I get unique record from mongodb?
问题
我有一个名为'myplace'的集合。它有以下字段：place_name、latitude、longitude、city、country。
我想要以字母"A"开头的所有城市。我尝试了以下代码：
type Place struct{
City string `bson:"City"`
}
var city_name []Place
err = coll.Find(bson.M{"city": bson.M{"$regex":"^a", "$options":"si"}}).All(&city_name)
它能够获取到所有结果。问题是，一些'myplace'文档中的城市名相同，所以返回了重复的城市名。
假设我有5个'myplace'，其中3个城市名为"Baton Rouge"，剩下的两个为"Trivandrum, Kochi"。当我尝试获取以字母"B"开头的城市时，它会返回3次"Baton Rouge"。
如何确保每个城市名都是唯一的呢？
提前感谢。
英文:
I have a collection named 'myplace'. It has the following fields: place_name, latitude, longitude, city, country.
I want all the cities that start with the letter "A". I tried the following:
type Place struct{
City string `bson: "City"`
}
For retrieving the result from the db:
var city_name []Place
err = coll.Find(bson.M{"city": bson.M{"$regex":"^a", "$options":"si"}}).All(&city_name)
It's getting all the results. The problem is that some of the 'myplace' documents have the same city, so it's returning duplicate city names.
Let's say I have 5 myplaces, 3 with the city name "Baton Rouge" and remaining having "Trivandrum, Kochi". When I try to get the city starting with "B", it's returning "Baton Rouge" 3 times.
How can I ensure each city_name is unique?
Thanks in advance
答案1
得分: 1
你可以使用Distinct方法，在shell中的写法如下：
db.foo.distinct("city", { "city" : { "$regex" : /^A/i } });
在Go语言中的写法如下：
var result []string
err = c.Find(bson.M{"city": bson.M{"$regex":"^a","$options":"si"}}).Distinct("city", &result)
if err != nil {
log.Fatal(err)
}
fmt.Println(result)
英文:
You can use the Distinct method, in the shell it will look like :
db.foo.distinct( "city", { "city" : { "$regex" : /^A/i } } );
In Go:
var result []string
err = c.Find( bson.M{"city": bson.M{"$regex":"^a","$options":"si"}} ).Distinct("city", &result)
if err != nil {
log.Fatal(err)
}
fmt.Println( result )
答案2
得分: 0
你可以使用Distinct方法来实现：
err = coll.Find(bson.M{"city": bson.M{"$regex":"^a", "$options":"si"}}).Distinct("city", &city_name)
..这里假设city_name实际上是一个切片。
英文:
You can use Distinct:
err = coll.Find(bson.M{"city": bson.M{"$regex":"^a", "$options":"si"}}).Distinct("city", &city_name)
..this assumes that city_name is actually a slice.
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