PyMongo で内部結合

PyMongo を使った内部結合の実装です。classics テーブル、baroque テーブルの内部結合を キー composer_id で照らし合わせたものです。

外部結合なら $match の部分なしで結果がとれます。

_id で照らし合わせる場合、ObjectId(id) で合わせるか文字列へ変換するか気を付ける必要があります。

{"_id":"5d355b602f3e9e3268f12a20","composer_id":"5d2b80272f3e9e25e0eadccf"}

view raw baroque hosted with ❤ by GitHub

	from flask_pymongo import PyMongo
	classics = list(mongo.db.classics.aggregate(
	[
	{ "$lookup" :
	{
	"from":"baroque",
	"localField":"composer_id",
	"foreignField":"composer_id",
	"as":"baroqueid"
	}
	}
	,
	{ "$match" :
	{
	"baroqueid": {"$ne": []}
	}
	}
	]
	))

view raw baroque.py hosted with ❤ by GitHub

	{
	"_id":"5d2fdb532f3e9e25b046aed1",
	"title":"01 Track 1.wma",
	"path":"\\Music\\BACH.Johann.Sebastian\\Bach Brandenburg Concertos Nos. 1-4, 6\\01 Track 1.wma",
	"composer":"BACH.Johann.Sebastian",
	"work":"Bach Brandenburg Concertos Nos. 1-4, 6","composer_id":"5d2b80272f3e9e25e0eadccf"
	}

view raw classics hosted with ❤ by GitHub