I am a newbie to mongo, I have a collection in my mongodb, To test a feature in my project I need to update database with some random data.I need a script to do that. by identifying the datatype of the field script should fill up the data automatically.
suppose I have the fields in the collection:
id, name, first_name, last_name, current_date, user_income etc.
Since the my questions are as follows:
1. Can we get all field names of a collection with their data types?
2. Can we generate a random value of that data type in mongo shell?
3. how to set the values dynamically to store random data.
I am frequently putting manually to do this.
1. Can we get all field names of a collection with their data types?
mongodb collections are schema-less, which means each document (row in relation database) can have different fields. When you find a document from a collection, you could get its fields names and data types.
2. Can we generate a random value of that data type in mongo shell?
3. how to set the values dynamically to store random data.
mongo shell use JavaScript, you may write a js script and run it with mongo the_js_file.js. So you could generate a random value in the js script.
It's useful to have a look at the mongo JavaScript API documentation and the mongo shell JavaScript Method Reference.
Other script language such as Python can also do that. mongodb has their APIs too.
Related
I am trying to sort a field, but I need to do it like how mysql does and specify the value,
instead of field number sory by -1, 4 3 2 1.
I need to sort it by 2,1,3,4.
is this possible in mongodb?
This is not possible in MongoDB. MongoDB doesn't know which and how many fields exist in a particular document unless the document is retrieved.
Hence MongoDB practically cannot give numbers to specific fields.
MongoDB is a JSON-style data store. The documents stored in the
database can have varying sets of fields, with different types for
each field.
In Databases the number and types of the column is fixed by particular table definition and it's easier for a database system to give numbers to the columns.
I'm trying to migrate data from Parse to a new project that uses Mongo as its database (without Parse/Parse Server). Since the schemas are different between the two projects, I'm manually writing a migration script to achieve this.
As I understand it, Parse appears to use 10-character-long IDs for their objects (combinations of digits, lower-case letters, and upper-case letters), while Mongo uses 24-character-long IDs (12 bytes represented as hex).
Right now, when migrating data for a document from the old project to the new one, I'm using a function that converts the Parse ID to a unique Mongo ObjectId (it converts each character to a 2-digit hex value, then pads the 20-character string with 4 zeroes).
Is this a good approach? I'm avoiding using Mongo's automatic ObjectId generation in case I ever need to re-migrate any of the old Parse documents and find the matching document in the new database. I know automatically generated ObjectIds in Mongo also embed some other information like creation dates, but I don't think this would be important and I can just use my custom ObjectId generator? However, I'm not sure about the implications for performance/if I'm just going about this migration the wrong way.
The approach i recommend is letting Mongo auto-generate the ids and then storing Parse's ids in a new field called parseID for future reference if needed.
For example:
PARSE DATA:
"_id": ObjectId(1234567890),
"title": "Mongo Migrate",
"description": "Migrating from Parse to Mongo"
MONGO DATA:
"_id": ObjectId(1ad83e4k2ab8e0daa8ebde7), //mongo generated
"parseId":ObjectId(1234567890),
"title": "Mongo Migrate",
"description": "Migrating from Parse to Mongo"
Then if you need to match a document between the two databases later, you can write a script that goes along the lines of Parse.find({"_id": Mongo.parseId}).....
MongoDB uses _id as primary key by default. _id has to be unique to avoid collision. The way you are generating unique ObjectId to _id is fine. As long as they are unique, you could even reduce the 20-character pad to save space.
I'm trying to build routes in my Meteor app. Routing works perfectly fine but getting information from db with route path just doesn't work. I create my page specific routes with this:
FlowRouter.route('/level/:id'...
This route takes me to related template without a problem. Then I want to get some data from database that belong to that page. In my template helpers I get my page's id with this:
var id = FlowRouter.getParam('id');
This gets the ObjectID() but in string format. So I try to find that ObjectID() document in the collection with this:
Levels.findOne({_id: id});
But of course documents doesn't have ObjectIDs in string format (otherwise we wouldn't call it "object"id). Hence, it brings an undefined error. I don't want to deal with creating my own _ids so is there anything I can do about this?
PS: Mongo used to create _ids with plain text. Someting like I would get with _id._str now but all of a sudden, it generates ObjectID(). I don't know why, any ideas?
MongoDB used ObjectIds as _ids by default and Meteor explicitly sets GUID strings by default.
Perhaps you inserted using a meteor shell session in the past and now used a mongo shell/GUI or a meteor mongo prompt to do so, which resulted in ObjectIds being created.
If this happens in a development environment, you could generate the data again.
Otherwise, you could try to generate new _ids for your data using Meteor.uuid().
If you want to use ObjectId as the default for a certain collection, you can specify the idGeneration option to its constructor as 'MONGO'.
If you have the string content of an ObjectId and want to convert it, you can issue
let _id = new Mongo.ObjectID(my23HexCharString);
I'm beginner with mongoDB. i want to know is there any way to load predefined schema to mongoDB? ( for example like cassandra that use .cql file for this purpose)
If there is, please intruduce some document about structure of that file and way for restoring.
If there is not, how i can create an index only one time when I create a collection. I think it is wrong if i create index every time I call insert method or run my program.
p.s: I have a multi-threaded program that every thread insert and update my mongo collection. I want to create index only one time.
Thanks.
To create an index on a collection you need to use ensureIndex command. You need to only call it once to create an index on a collection.
If you call ensureIndex repeatedly with the same arguments, only the first call will create an index, all subsequent calls will have no effect.
So if you know what indexes you're going to use for your database, you can create a script that will call that command.
An example insert_index.js file that creates 2 indexes for collA and collB collections:
db.collA.ensureIndex({ a : 1});
db.collB.ensureIndex({ b : -1});
You can call it from a shell like this:
mongo --quiet localhost/dbName insert_index.js
This will create those indexes on a database named dbName on your localhost. It's worth noticing that if your database and/or collections are not yet created, this will create both the database and the collections for which you're adding the indexes.
Edit
To clarify a little bit. MongoDB is schemaless so you can't restore it's schema.
You can only create indexes and collections (by using createCollection helper).
MongoDB is basically schemaless so there is no definition of a schema or namespaces to be restored.
In the case of indexes, these can be created at any time. There does not need to be a collection present or even the required fields for the index as this will all be sorted out as the collections are created and when documents are inserted that matches the defined fields.
Commands to create an index are generally the same with each implementation language, for example:
db.collection.ensureIndex({ a: 1, b: -1 })
Will define the index on the target collection in the target database that will reference field "a" and field "b", the latter in descending order. This will happen even if the collection or even the database does not exist as yet, or in fact will establish a blank namespace in that case.
Subsequent calls to the same index creation method do not actually re-create the index. Where the same index is specified to one that already exists it is effectively skipped as a "no-operation".
As such, you can simply feed all your required index creation statements at application startup and anything that is not already present will be created. Anything that already exists will be left alone.
I have a number of different documents in a mongo collection.
The attrs are all numeric values. I don't know apriori what the fieldnames are (I do but they can vary from doc to doc).
I want to write a program that
a) gets all the unique fieldnames in a collection
b) finds the max and min value of each field in the collection
and then reports it in a tabular form with rows "fieldname, maxvalue, minvalue" or in JSON that is equivalent. I am using pymongo but I don't have to, ruby or js or even java driver is fine.
How do I get programmatic access to the list of unique fieldnames in a collection? That's
the major question. I can manage the rest.
Either you main the list of used key inside your application as part of your application logic in some document inside the same collection or a meta-collection yourself or you have to iterate over all documents to figure out the list of keys...there is nothing in MongoDB helping you here since MongoDB is schemaless.