2017-11-22 20:24
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Here is a statement where Limit() precedes Sort()...

var result Candle
dao.c.Find(bson.M{"symbol": "USD"}).Limit(1).Sort("-time").One(&result);

... and here is a statement where Limit() comes after Sort():

var result Candle
dao.c.Find(bson.M{"symbol": "USD"}).Sort("-time").Limit(1).One(&result);

Is there any performance difference between the statements above?

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1条回答 默认 最新

  • dqx76962
    dqx76962 2017-11-23 08:47

    We might answer regarding the mgo package and MongoDB itself.

    In mgo

    The Query.Limit() and Query.Sort() methods just operate on the Query object locally, and once you setup the query, you execute it e.g. with Query.One() or Query.All(). The order in which you called the methods to set it up is not stored and does not matter.

    In MongoDB

    Quoting from MongoDB doc: Combine Cursor Methods:

    The following statements chain cursor methods limit() and sort():

    db.bios.find().sort( { name: 1 } ).limit( 5 )
    db.bios.find().limit( 5 ).sort( { name: 1 } )

    The two statements are equivalent; i.e. the order in which you chain the limit() and the sort() methods is not significant. Both statements return the first five documents, as determined by the ascending sort order on ‘name’.

    So there is no difference, they are equivalent and thus have the same performance.

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