how to get all collections name by filter?

Question

how to get all collections name by filter?

recently i want to use mongodb driver to get all collections name by filter.

"Admin",
"Config",
"Event",
"event12345678901234567890123456789012",
"system.indexes"

above is the all collections name ,but i only want to show collection which start with 'event',and i found documents have a filter params,but the documents don't show any usage and filter rule,so is there anyone know how to use it?

node.js
mongodb

Answer 1

Since getCollectionNames() is based on querying db.system.namespaces:

The <database>.system.namespaces collection contains information about all of the database’s collections. Additional namespace metadata exists in the database.ns files and is opaque to database users.

> db.getCollectionNames;
function (){
    var all = [];

    var nsLength = this._name.length + 1;

    var c = this.getCollection( "system.namespaces" ).find();
    while ( c.hasNext() ){
        var name = c.next().name;

        if ( name.indexOf( "$" ) >= 0 && name.indexOf( ".oplog.$" ) < 0 )
            continue;

        all.push( name.substring( nsLength ) );
    }

    return all.sort();
}

You can filter db.system.namespaces manually using $regex:

db.system.namespaces.find({'name': {"$regex": /^foo.Event\w*$/, "$options": "-i"}});

where foo is a database name, -i helps to make a case-insensitive search.

Demo (from "mongo shell"):

> db.system.namespaces.find();
{ "name" : "foo.system.indexes" }
{ "name" : "foo.system.users.$_id_" }
{ "name" : "foo.system.users.$user_1_userSource_1" }
{ "name" : "foo.system.users" }
{ "name" : "foo.foo.$_id_" }
{ "name" : "foo.foo" }
{ "name" : "foo.test.$_id_" }
{ "name" : "foo.test", "options" : { "create" : "test" } }
{ "name" : "foo.Config.$_id_" }
{ "name" : "foo.Config", "options" : { "create" : "Config" } }
{ "name" : "foo.Event.$_id_" }
{ "name" : "foo.Event", "options" : { "create" : "Event" } }
{ "name" : "foo.event12345678901234567890123456789012.$_id_" }
{ "name" : "foo.event12345678901234567890123456789012", "options" : { "create" : "event12345678901234567890123456789012" } }
{ "name" : "foo.Admin.$_id_" }
{ "name" : "foo.Admin", "options" : { "create" : "Admin" } }

> db.system.namespaces.find({'name': {"$regex": /^foo.Event\w*$/, "$options": "-i"}});
{ "name" : "foo.Event", "options" : { "create" : "Event" } }
{ "name" : "foo.event12345678901234567890123456789012", "options" : { "create" : "event12345678901234567890123456789012" } }