Accessing nested document in mongodb using mgo

例えばこんな documentあります

{
    "_id" : ObjectId("56149e20cc1cb46e80170809"),
    "name_jp" : "",
    "name_en" : "app1",
    "application_id" : "56149e20cc1cb46e8017080a",
    "fields" : [
        {
            "colnameen" : "age",
            "colnamejp" : "age",
            "id" : "g9C3r",
            "name" : "age",
            "type" : "string"
        }
    ],
    "statuses" : [

        {
            "_id" : ObjectId("56149e20cc1cb46e80170830"),
            "name_jp" : "deleted",
            "name_en" : "deleted",
            "actions" : [ ]
        },
        {
            "_id" : ObjectId("56149e20cc1cb46e80170832"),
            "name_jp" : "checking",
            "name_en" : "checking",
            "actions" : [
                {
                    "_id" : ObjectId("56149e38cc1cb46e80170833"),
                    "name_jp" : "",
                    "name_en" : "new checking",
                    "name" : "",
                    "next_status" : "56149e20cc1cb46e8017082f",
                    "update_fields" : [
                        {
                            "field_id" : "g9C3r",
                            "is_mandatory" : false,
                            "is_editable" : true
                        },
                        {
                            "field_id" : "9p3SY",
                            "is_mandatory" : false,
                            "is_editable" : true
                        }
                    ]
                },
                {
                    "_id" : ObjectId("56149e52cc1cb46e80170834"),
                    "name_jp" : "",
                    "name_en" : "delete checking",
                    "name" : "",
                    "next_status" : "56149e20cc1cb46e80170830",
                    "update_fields" : [
                        {
                            "field_id" : "g9C3r",
                            "is_mandatory" : false,
                            "is_editable" : true
                        },
                        {
                            "field_id" : "9p3SY",
                            "is_mandatory" : false,
                            "is_editable" : true
                        },
                        {
                            "field_id" : "MPd75",
                            "is_mandatory" : false,
                            "is_editable" : true
                        }
                    ]
                }
            ]
        }
    ],
    "unread" : 0,
    "created_at" : ISODate("2015-10-07T04:22:56.671Z"),
    "updated_at" : ISODate("2015-10-07T04:22:56.671Z")
}

statuses.actions._id=ObjectId("56149e38cc1cb46e80170833") select したい時に、どうしたらいい？

{
                    "_id" : ObjectId("56149e38cc1cb46e80170833"),
                    "name_jp" : "",
                    "name_en" : "new checking",
                    "name" : "",
                    "next_status" : "56149e20cc1cb46e8017082f",
                    "update_fields" : [
                        {
                            "field_id" : "g9C3r",
                            "is_mandatory" : false,
                            "is_editable" : true
                        },
                        {
                            "field_id" : "9p3SY",
                            "is_mandatory" : false,
                            "is_editable" : true
                        }
                    ]
                }

Try find #1

mongos> db.data_stores.find({_id:ObjectId("56149e20cc1cb46e80170809"),"statuses.actions._id":ObjectId("56149e38cc1cb46e80170833")},{"statuses.actions.$":1})

{
    "_id" : ObjectId("56149e20cc1cb46e80170809"),
    "statuses" : [
        {
            "_id" : ObjectId("56149e20cc1cb46e80170832"),
            "name_jp" : "checking",
            "name_en" : "checking",
            "actions" : [
                {
                    "_id" : ObjectId("56149e38cc1cb46e80170833"),
                    "name_jp" : "",
                    "name_en" : "new checking",
                    "name" : "",
                    "next_status" : "56149e20cc1cb46e8017082f",
                    "update_fields" : [
                        {
                            "field_id" : "g9C3r",
                            "is_mandatory" : false,
                            "is_editable" : true
                        },
                        {
                            "field_id" : "9p3SY",
                            "is_mandatory" : false,
                            "is_editable" : true
                        }
                    ]
                },
                {
                    "_id" : ObjectId("56149e52cc1cb46e80170834"),
                    "name_jp" : "",
                    "name_en" : "delete checking",
                    "name" : "",
                    "next_status" : "56149e20cc1cb46e80170830",
                    "update_fields" : [
                        {
                            "field_id" : "g9C3r",
                            "is_mandatory" : false,
                            "is_editable" : true
                        },
                        {
                            "field_id" : "9p3SY",
                            "is_mandatory" : false,
                            "is_editable" : true
                        },
                        {
                            "field_id" : "MPd75",
                            "is_mandatory" : false,
                            "is_editable" : true
                        }
                    ]
                }
            ]
        }
    ]
}

結果が大丈夫ですけど、不要なデータが含まります。使えない

Try aggregation framework #2

mongos> db.data_stores.aggregate([
{$match:{_id:ObjectId("56149e20cc1cb46e80170809")}},
{$unwind:"$statuses"},
{$unwind:"$statuses.actions"},
{$match:{"statuses.actions._id":ObjectId("56149e38cc1cb46e80170833")}}
]).pretty()

{
    "_id" : ObjectId("56149e20cc1cb46e80170809"),
    "name_jp" : "",
    "name_en" : "app1",
    "application_id" : "56149e20cc1cb46e8017080a",
    "fields" : [
        {
            "colnameen" : "age",
            "colnamejp" : "age",
            "id" : "g9C3r",
            "name" : "age",
            "type" : "string"
        },

    ],
    "statuses" : {
        "_id" : ObjectId("56149e20cc1cb46e80170832"),
        "name_jp" : "checking",
        "name_en" : "checking",
        "actions" : {
            "_id" : ObjectId("56149e38cc1cb46e80170833"),
            "name_jp" : "",
            "name_en" : "new checking",
            "name" : "",
            "next_status" : "56149e20cc1cb46e8017082f",
            "update_fields" : [
                {
                    "field_id" : "g9C3r",
                    "is_mandatory" : false,
                    "is_editable" : true
                },
                {
                    "field_id" : "9p3SY",
                    "is_mandatory" : false,
                    "is_editable" : true
                }
            ]
        }
    },
    "unread" : 0,
    "created_at" : ISODate("2015-10-07T04:22:56.671Z"),
    "updated_at" : ISODate("2015-10-07T04:22:56.671Z")
}

さすがaggregation framework。この結果が使えると思います。

mgoで書くとクエリが

    query := []bson.M{
        {"$match": bson.M{"_id": dataStoreID}},
        {"$unwind": "$statuses"},
        {"$unwind": "$statuses.actions"},
        {"$match": bson.M{
            "statuses.actions._id": actionID,
        }},
    }

    err := c.Pipe(query).One(&dt)