mongoDB array pagination

2020-02-07 10:01发布

问题:

I have a comment collection with Comment Text in array with its Metadata. I like to the pagination in the Comment Text Array. The pagination should allow me to get the "previous 5" or "next 5". What is the best way to do this in mongoDB with good performance.

   { "_id" : ObjectId( "502c706ac2e6777781a593f6" ),
      "commentType":"loc",
      "commentList" : [ 
{ "commentText" : "HelloComment",
  "commentTS" : Date( 1345165636344 ),
  "commentLoc" : { "commentlat" : 0,
    "commentlong" : 0 },
  "userInfo" : { "$ref" : "userProfile",
    "$id" : ObjectId( "4fd182d92b2a87f780c6bbe8" ) } }, 
{ "commentText" : "2222222",
  "commentTS" : Date( 1345165636344 ),
  "commentLoc" : { "commentlat" : 0,
    "commentlong" : 0 },
  "userInfo" : { "$ref" : "userProfile",
    "$id" : ObjectId( "4fd182d92b2a87f780c6bbe8" ) } }, 
{ "commentText" : "3333333",
  "commentTS" : Date( 1345165636344 ),
  "commentLoc" : { "commentlat" : 0,
    "commentlong" : 0 },
  "userInfo" : { "$ref" : "userProfile",
    "$id" : ObjectId( "4fd182d92b2a87f780c6bbe8" ) } }, 
{ "commentText" : "44444444",
  "commentTS" : Date( 1345165636344 ),
  "commentLoc" : { "commentlat" : 0,
    "commentlong" : 0 },
  "userInfo" : { "$ref" : "userProfile",
    "$id" : ObjectId( "4fd182d92b2a87f780c6bbe8" ) } }, 
{ "commentText" : "5555555",
  "commentTS" : Date( 1345165636344 ),
  "commentLoc" : { "commentlat" : 0,
    "commentlong" : 0 },
  "userInfo" : { "$ref" : "userProfile",
    "$id" : ObjectId( "4fd182d92b2a87f780c6bbe8" ) } }, 
{ "commentText" : "6666666",
  "commentTS" : Date( 1345165636344 ),
  "commentLoc" : { "commentlat" : 0,
    "commentlong" : 0 },
  "userInfo" : { "$ref" : "userProfile",
    "$id" : ObjectId( "4fd182d92b2a87f780c6bbe8" ) } }, 
    { "commentText" : "777777",
  "commentTS" : Date( 1345165636344 ),
  "commentLoc" : { "commentlat" : 0,
    "commentlong" : 0 },
  "userInfo" : { "$ref" : "userProfile",
    "$id" : ObjectId( "4fd182d92b2a87f780c6bbe8" ) } }, 
    { "commentText" : "888888",
  "commentTS" : Date( 1345165636344 ),
  "commentLoc" : { "commentlat" : 0,
    "commentlong" : 0 },
  "userInfo" : { "$ref" : "userProfile",
    "$id" : ObjectId( "4fd182d92b2a87f780c6bbe8" ) } }, 
    { "commentText" : "6666666",
  "commentTS" : Date( 1345165636344 ),
  "commentLoc" : { "commentlat" : 0,
    "commentlong" : 0 },
  "userInfo" : { "$ref" : "userProfile",
    "$id" : ObjectId( "4fd182d92b2a87f780c6bbe8" ) } }, 
{ "commentText" : "999999",
  "commentTS" : Date( 1345165668809 ),
  "commentLoc" : { "commentlat" : 0,
    "commentlong" : 0 },
  "userInfo" : { "$ref" : "userProfile",
    "$id" : ObjectId( "4fdeb271de26fd298262bb84" ) } }, 
{ "commentText" : "HelloComment",
  "commentTS" : Date( 1345749858601 ),
  "commentLoc" : { "commentlat" : 0,
    "commentlong" : 0 },
  "userInfo" : { "$ref" : "userProfile",
    "$id" : ObjectId( "4fdeb271de26fd298262bb84" ) } }, 
{ "commentText" : "NewTestforcomments",
  "commentTS" : Date( 1345750020526 ),
  "commentLoc" : { "commentlat" : 0,
    "commentlong" : 0 },
  "userInfo" : { "$ref" : "userProfile",
    "$id" : ObjectId( "4fdeb271de26fd298262bb84" ) } } ],
   } } 

Thanks for your help.

回答1:

You can do this with $slice: http://www.mongodb.org/display/DOCS/Retrieving+a+Subset+of+Fields#RetrievingaSubsetofFields-RetrievingaSubrangeofArrayElements

There's also a js test example of slice here, with several examples: https://github.com/mongodb/mongo/blob/master/jstests/slice1.js

So, findOne, combined with $slice, is probably the way to go.

Without more info about the language you're using, I think that's the deepest I can go.