MongoDB Aggregation Framework fun: ordering fabric for flags

One of the really cool, well designed features in MongoDB is the aggregation framework. Basically it is the feature that brings MongoDB query language on par with SQL in feature richness. Most importantly, it fully supports sharding for scale-out and parallel processing. I've had a lot of fun with it.

Last night I accidentally came up with a fun exercise that you can solve with a nice aggregation framework pipeline. I'll present it as a challenge, feel free to suggest answers in comments. I'll share my answer next week.


Suppose you work in a flag factory, and you have received the following orders:

> db.flags.find().pretty()
{
	"_id" : ObjectId("52a7189ecd4dd732cd060201"),
	"country" : "Finland",
	"colors" : [
		{
			"color" : "blue",
			"fabric_units" : 2
		},
		{
			"color" : "white",
			"fabric_units" : 3
		}
	],
	"num_flags" : 3
}
{
	"_id" : ObjectId("52a718bccd4dd732cd060202"),
	"country" : "Sweden",
	"colors" : [
		{
			"color" : "blue",
			"fabric_units" : 2
		},
		{
			"color" : "yellow",
			"fabric_units" : 2
		}
	],
	"num_flags" : 1
}
{
	"_id" : ObjectId("52a718c2cd4dd732cd060203"),
	"country" : "Finland",
	"colors" : [
		{
			"color" : "blue",
			"fabric_units" : 2
		},
		{
			"color" : "white",
			"fabric_units" : 3
		}
	],
	"num_flags" : 1
}
{
	"_id" : ObjectId("52a71923cd4dd732cd060204"),
	"country" : "Norway",
	"colors" : [
		{
			"color" : "red",
			"fabric_units" : 3
		},
		{
			"color" : "blue",
			"fabric_units" : 2
		},
		{
			"color" : "white",
			"fabric_units" : 1
		}
	],
	"num_flags" : 2
}
{
	"_id" : ObjectId("52a7195bcd4dd732cd060205"),
	"country" : "Åland",
	"colors" : [
		{
			"color" : "blue",
			"fabric_units" : 3
		},
		{
			"color" : "red",
			"fabric_units" : 2
		},
		{
			"color" : "yellow",
			"fabric_units" : 1
		}
	],
	"num_flags" : 1
}

You need to order an appropriate amount of fabric, of each color, to produce the number of flags given in num_flags. What is the aggregation framework query that will tell you how much fabric, of each color, do you need?

The answer has now been posted here.

Add new comment

The content of this field is kept private and will not be shown publicly. Cookie & Privacy Policy
  • No HTML tags allowed.
  • External and mailto links in content links have an icon.
  • Lines and paragraphs break automatically.
  • Web page addresses and email addresses turn into links automatically.
  • Use [fn]...[/fn] (or <fn>...</fn>) to insert automatically numbered footnotes.
  • Each email address will be obfuscated in a human readable fashion or, if JavaScript is enabled, replaced with a spam resistent clickable link. Email addresses will get the default web form unless specified. If replacement text (a persons name) is required a webform is also required. Separate each part with the "|" pipe symbol. Replace spaces in names with "_".
About the bookAbout this siteAcademicAmazonBeginnersBooksBuildBotBusiness modelsbzrCassandraCloudcloud computingclsCommunitycommunityleadershipsummitConsistencycoodiaryCopyrightCreative CommonscssDatabasesdataminingDatastaxDevOpsDrizzleDrupalEconomyelectronEthicsEurovisionFacebookFrosconFunnyGaleraGISgithubGnomeGovernanceHandlerSocketHigh AvailabilityimpressionistimpressjsInkscapeInternetJavaScriptjsonKDEKubuntuLicensingLinuxMaidanMaker cultureMariaDBmarkdownMEAN stackMepSQLMicrosoftMobileMongoDBMontyProgramMusicMySQLMySQL ClusterNerdsNodeNoSQLodbaOpen ContentOpen SourceOpenSQLCampOracleOSConPAMPPatentsPerconaperformancePersonalPhilosophyPHPPiratesPlanetDrupalPoliticsPostgreSQLPresalespresentationsPress releasesProgrammingRed HatReplicationSeveralninesSillySkySQLSolonStartupsSunSybaseSymbiansysbenchtalksTechnicalTechnologyThe making ofTungstenTwitterUbuntuvolcanoWeb2.0WikipediaWork from HomexmlYouTube