Mongo shell script and sample documents used for my aggregation talks 12/2011

aggregation.js

// make sure we're using the right db; this is the same as "use aggdb;" in shell
db = db.getSiblingDB("aggdb");

// simple projection
var p1 = db.article.aggregate({
    $project: { tags: 1, pageViews: 1 }
});

// unwinding an array
var u1 = db.article.aggregate({
    $unwind: "$tags"
});

// combining pipeline operations
var p2 = db.article.aggregate(
    { $project: {
          author: 1
        , tags: 1
        , pageViews: 1
    }}
  , { $unwind: "$tags" }
);

// pulling values out of subdocuments
var p3 = db.article.aggregate(
    { $project: {
          otherfoo: "$other.foo"
        , otherbar: "$other.bar"
    }}
);


// projection includes a computed value
var p4 = db.article.aggregate(
    { $project: {
          author: 1
        , daveWroteIt: { $eq: ["$author", "dave"] }
    }}
);

// projection includes a virtual (fabricated) document
var p5 = db.article.aggregate(
    { $project: {
          author: 1
        , pageViews: 1
        , tags: 1
      }
    }
  , { $unwind: "$tags" }
  , { $project: {
          author: 1
        , subDocument: { foo: "$pageViews", bar: "$tags"  }
      }
    }
);

// nested computed expression; $ifNull
var p7 = db.article.aggregate(
    { $project: {
        theSum: {
            $add: ["$pageViews", { $ifNull: ["$other.foo", "$other.bar"] }]
        }
      }
    }
);

// dotted path inclusion; _id exclusion
var p8 = db.article.aggregate(
    { $project: {
          _id: 0
        , author: 1
        , tags: 1
        , "comments.author": 1
      }
    }
);

// simple sort
var p10 = db.article.aggregate({ $sort: { title: 1 }})

// dates
var p19 = db.article.aggregate(
    { $project: {
          authors: 1
        , seconds: {$second: "$posted"}
        , minutes: {$minute: "$posted"}
        , hour: {$hour: "$posted"}
        , dayOfYear: {$dayOfYear: "$posted"}
        , dayOfMonth: {$dayOfMonth: "$posted"}
        , dayOfWeek: {$dayOfWeek: "$posted"}
        , month: {$month: "$posted"}
        , week: {$week: "$posted"}
        , year: {$year: "$posted"}
        , posted: 1
      }
    }
);

// ternary conditional ($cond) operator
var p21 = db.article.aggregate(
    { $project: {
          _id: 0
        , author: 1
        , pageViews: {
              $cond: [
                  { $eq: ["$author", "dave"]} // if
                , { $add:["$pageViews", 1000]}// then
                , "$pageViews"                // else
              ]
          }
      }
    }
);

// simple matching
var m1 = db.article.aggregate({ $match: { author: "dave" }});

// combining matching with a projection
var m2 = db.article.aggregate(
    { $project: {
          title: 1
        , author: 1
        , pageViews: 1
        , tags: 1
        , comments: 1
      }
    }
  , { $unwind: "$tags" }
  , { $match: { tags: "nasty" }}
);

// grouping
var g1 = db.article.aggregate(
    { $project: {
          author: 1
        , tags: 1
        , pageViews: 1
      }
    }
  , { $unwind: "$tags" }
  , { $group: {
          _id: "$tags"
        , docsByTag: { $sum: 1 }
        , viewsByTag: { $sum: "$pageViews" }
        , mostViewsByTag: { $max: "$pageViews" }
        , avgByTag: { $avg: "$pageViews" }
      }
    }
);

// $addToSet as an accumulator; can pivot data
var g5 = db.article.aggregate(
    { $project: {
          author: 1
        , tags: 1
      }
    }
  , { $unwind: "$tags" }
  , { $group: {
          _id: "$tags"
        , authors: { $addToSet: "$author" }
      }
    }
);

articles.js

/* sample articles for aggregation demonstrations */

// make sure we're using the right db; this is the same as "use mydb;" in shell
db = db.getSiblingDB("aggdb");
db.article.drop();

db.article.save( {
    title : "this is my title" , 
    author : "bob" , 
    posted : new Date(1079895594000) , 
    pageViews : 5 , 
    tags : [ "fun" , "good" , "fun" ] ,
    comments : [ 
        { author :"joe" , text : "this is cool" } , 
        { author :"sam" , text : "this is bad" } 
    ],
    other : { foo : 5 }
});

db.article.save( {
    title : "this is your title" , 
    author : "dave" , 
    posted : new Date(4121381470000) , 
    pageViews : 7 , 
    tags : [ "fun" , "nasty" ] ,
    comments : [ 
        { author :"barbara" , text : "this is interesting" } , 
        { author :"jenny" , text : "i like to play pinball", votes: 10 } 
    ],
    other : { bar : 14 }
});

db.article.save( {
    title : "this is some other title" , 
    author : "jane" , 
    posted : new Date(978239834000) , 
    pageViews : 6 , 
    tags : [ "nasty" , "filthy" ] ,
    comments : [ 
        { author :"will" , text : "i don't like the color" } , 
        { author :"jenny" , text : "can i get that in green?" } 
    ],
    other : { bar : 14 }
});