Pipeline operations

$match

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

$match and projection

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

$project

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

example unwind

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 }
});

match

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

match and projection

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

project

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

unwind example

    title : "this is your title" , 
    author : "dave" , 
    posted : new Date(4121381470000) , 
    pageViews : 7 , 
    tags : [ "fun" ] ,
    
});

    title : "this is your title" , 
    author : "dave" , 
    posted : new Date(4121381470000) , 
    pageViews : 7 , 
    tags : [ "nasty" ] ,
    
});


    title : "this is some other title" , 
    author : "jane" , 
    posted : new Date(978239834000) , 
    pageViews : 6 , 
    tags : [ "nasty"] ,
});

    title : "this is some other title" , 
    author : "jane" , 
    posted : new Date(978239834000) , 
    pageViews : 6 , 
    tags : [ "filthy"] ,
});

unwinding

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