$concat string with $cond in mongodb aggregation

Question

[
{
    "user_id" : 12453,
    "profile_type" : "demo_type_1",
    "records" : [
        {
            "type" : "typ_11",
            "value" : {
                "high" : 115,
                "low" : 78
            },
            "_meta" : {
                "data_type" : "text"
            }
        },
        {
            "type" : "type_1",
            "files" : [
                {
                    "title" : "path_prescription_1",
                    "url" : "/file_name.extension"
                },
                {
                    "title" : "path_prescription_2",
                    "url" : "/file_name__1.extension"
                }
            ],
            "_meta" : {
                "data_type" : "file"
            }
        }
    ]
},
{
    "user_id" : 12455,
    "profile_type" : "demo_type_1",
    "records" : [
        {
            "type" : "typ_11",
            "value" : {
                "high" : 115,
                "low" : 78
            },
            "_meta" : {
                "data_type" : "text"
            }
        },
        {
            "type" : "type_1",
            "files" : [
                {
                    "title" : "path_prescription_1",
                    "url" : "/file_name.extension"
                },
                {
                    "title" : "path_prescription_2",
                    "url" : "/file_name__1.extension"
                }
            ],
            "_meta" : {
                "data_type" : "file"
            }
        }
    ]
},
...
]

i want to append prefix the url value to make it an absolute path while retrieving from the database only when the _meta fields data_type is file not for text. The is stored in the above format and retrieved in the same format only with the appended url.

is there any way to do this by using aggregation pipeline ?

Answer 1

You can try using $addFields like this:

db.getCollection('test').aggregate(

[

{
    $unwind: {
        path:"$records",

        preserveNullAndEmptyArrays: true
        }
},

{
    $unwind: {
        path:"$records.files",

        preserveNullAndEmptyArrays: true
        }
},

{
    $addFields: {
        "records.files.url":{
             $cond: {
                    if: {
                      $eq: ['$records.files', undefined]
                    },
                    then: null,
                    else: {$concat: ["some_prefix", "$records.files.url"]}
              }

            }
        }

    }

]

)

This will give you:

/* 1 */
{
    "_id" : ObjectId("5b6c484b9a8ea6a11c508520"),
    "user_id" : 12453.0,
    "profile_type" : "demo_type_1",
    "records" : {
        "type" : "typ_11",
        "value" : {
            "high" : 115.0,
            "low" : 78.0
        },
        "_meta" : {
            "data_type" : "text"
        },
        "files" : {
            "url" : null
        }
    }
}

/* 2 */
{
    "_id" : ObjectId("5b6c484b9a8ea6a11c508520"),
    "user_id" : 12453.0,
    "profile_type" : "demo_type_1",
    "records" : {
        "type" : "type_1",
        "files" : {
            "title" : "path_prescription_1",
            "url" : "some_prefix/file_name.extension"
        },
        "_meta" : {
            "data_type" : "file"
        }
    }
}

/* 3 */
{
    "_id" : ObjectId("5b6c484b9a8ea6a11c508520"),
    "user_id" : 12453.0,
    "profile_type" : "demo_type_1",
    "records" : {
        "type" : "type_1",
        "files" : {
            "title" : "path_prescription_2",
            "url" : "some_prefix/file_name__1.extension"
        },
        "_meta" : {
            "data_type" : "file"
        }
    }
}

/* 4 */
{
    "_id" : ObjectId("5b6c484b9a8ea6a11c508521"),
    "user_id" : 12455.0,
    "profile_type" : "demo_type_1",
    "records" : {
        "type" : "typ_11",
        "value" : {
            "high" : 115.0,
            "low" : 78.0
        },
        "_meta" : {
            "data_type" : "text"
        },
        "files" : {
            "url" : null
        }
    }
}

/* 5 */
{
    "_id" : ObjectId("5b6c484b9a8ea6a11c508521"),
    "user_id" : 12455.0,
    "profile_type" : "demo_type_1",
    "records" : {
        "type" : "type_1",
        "files" : {
            "title" : "path_prescription_1",
            "url" : "some_prefix/file_name.extension"
        },
        "_meta" : {
            "data_type" : "file"
        }
    }
}

/* 6 */
{
    "_id" : ObjectId("5b6c484b9a8ea6a11c508521"),
    "user_id" : 12455.0,
    "profile_type" : "demo_type_1",
    "records" : {
        "type" : "type_1",
        "files" : {
            "title" : "path_prescription_2",
            "url" : "some_prefix/file_name__1.extension"
        },
        "_meta" : {
            "data_type" : "file"
        }
    }
}

But remember to ignore records.files.url field when the record is type text.