dpysrta21239
dpysrta21239
2017-10-17 15:49

将收藏转换为使用mgo封顶

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I would like to convert a mongo collection to capped using gopkg.in/mgo.v2.

I am able to create a capped collection from scratch - as follows:

# Create a Capped Collection
sess.DB("").C("my_collection").Create(&mgo.CollectionInfo{Capped: true, MaxBytes: tenMB, MaxDocs: 10})

I can't work out how to get the stats for an existing collection or how to run convertToCapped command.

Step 1 - Get Collection Stats:

# Mongo
db.getCollection('my_collection').stats();

# mgo // I need to find out how to do this.

Step 2 - Convert to Capped

# Mongo
db.runCommand({"convertToCapped": "my_collection", size: 1000000});

# mgo // I need to find out how to do this.
if err := sess.DB("").Run(bson.D{{"convertToCapped", "my_collection"}, {"size", "1000"}}, nil); err != nil {
        println(err.Error()) // invalid command spec
        os.Exit(1)
}
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1条回答

  • douwei3172 douwei3172 4年前

    1. Get Collection Stats

    This is not part of the mgo package, but it is available as a runnable MongoDB command: collStats.

    Running collStats with mgo:

    var doc bson.M
    err := mgr.sess.DB("").Run(bson.D{
        {Name: "collStats", Value: "my_collection"},
    }, &doc)
    if err != nil {
        fmt.Println("Error:", err)
        return
    }
    
    fmt.Println("Result:", doc)
    fmt.Println("Capped:", doc["capped"])
    // Acquire capped info as a bool value:
    capped, ok := doc["capped"].(bool)
    if ok {
        fmt.Println("Capped bool value:", capped)
    }
    

    Example output (veeeeeeery long so chunked):

    Result: map[ok:1 size:36 storageSize:4096 totalIndexSize:4096  ...chunked...]
    Capped: true
    Capped bool value: true
    

    2. Converting to Capped

    The simple problem with your attempt is that the value of the "size" parameter must be a number and not a string. Quoting from the convertToCapped doc:

    The command has the following syntax:

      { convertToCapped: <collection>, size: <capped size> }
    

    convertToCapped takes an existing collection (<collection>) and transforms it into a capped collection with a maximum size in bytes, specified by the size argument (<capped size>).

    Correct version:

    var doc bson.M
    err := mgr.sess.DB("").Run(bson.D{
        {Name: "convertToCapped", Value: "my_collection"},
        {Name: "size", Value: 1<<20}, // 1 MB
    }, &doc)
    if err != nil {
        fmt.Println("Error:", err)
        return
    }
    
    fmt.Println("Result:", doc)
    

    Example output:

    Result: map[ok:1]
    
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