**MongoDB** creates databases and collections automatically for you if they don&#39;t exist already. 

For using python library with MongoDB, check out this **[documentation][1]**.
&gt; **Warning**:
&gt; the example is based on Pymongo **2.1**.
&gt; If you&#39;re using Pymongo **3.4**, check **[this doc][2]**.

    from pymongo import Connection
    connection = Connection()
    db = connection[&#39;test-database&#39;]
    collection = db[&#39;test-collection&#39;]

So here you can use any name for database and collection. 


  [1]: http://api.mongodb.org/python/2.1/tutorial.html
  [2]: https://api.mongodb.com/python/current/tutorial.html

This is Mongodb 3.4 Version:

    from pymongo import MongoClient
    client = MongoClient()
    db = client.primer
    coll = db.dataset

&gt; neither the database nor the collection are created until you attempt
&gt; to write a document.

Document: [Python Driver (PyMongo)][1]

 


  [1]: https://docs.mongodb.com/getting-started/python/client/

Needed to create a collection without inserting the documents in order to be able to set validators first.

Luckily the pymongo Database object defines [create_collection](https://pymongo.readthedocs.io/en/stable/api/pymongo/database.html#pymongo.database.Database.create_collection) method:

&gt; `create_collection(name, codec_options=None, read_preference=None, write_concern=None, read_concern=None, session=None, **kwargs)`
&gt;
&gt; Create a new Collection in this database.
&gt;
&gt; Normally collection creation is automatic. This method should only be used to specify options on creation. CollectionInvalid will be raised if the collection already exists.
&gt; 
&gt; ...
&gt; 
&gt; Changed in version 3.11: This method is now supported inside
&gt; multi-document transactions with MongoDB 4.4+.
&gt; 
&gt; Changed in version 3.6: Added session parameter.
&gt; 
&gt; Changed in version 3.4: Added the collation option.
&gt; 
&gt; Changed in version 3.0: Added the codec_options, read_preference, and
&gt; write_concern options.
&gt; 
&gt; Changed in version 2.2: Removed deprecated argument: options

	(SELECT COUNT(motorbike.`owner_id`) as count,owner.`name`,transport.`type` FROM transport,owner,motorbike WHERE transport.type=&#39;motobike&#39;
	AND owner.`owner_id`=motorbike.`owner_id`
	AND transport.`type_id`=motorbike.`motorbike_id` GROUP BY motorbike.owner_id)
	UNION ALL
	(SELECT COUNT(car.`owner_id`) as count,owner.`name`,transport.`type` FROM transport,owner,car WHERE transport.type=&#39;car&#39;
	AND owner.`owner_id`=car.`owner_id`
	AND transport.`type_id`=car.`car_id` GROUP BY car.`owner_id`)


The query above returns a result like this below,

    count          name
    1              Linda
    2              Mary
    1              Steve
    1              Linda

This query is to count how many transport that owned by an owner. Linda have one car and one motorcycle,so the result should:

    count          name
    2              Linda
    2              Mary
    1              Steve

I have tried this query,but return error:


	(SELECT COUNT(motorbike.`owner_id`),owner.`name`,transport.`type` FROM transport,owner,motorbike WHERE transport.type=&#39;motobike&#39;
	AND owner.`owner_id`=motorbike.`owner_id`
	AND transport.`type_id`=motorbike.`motorbike_id`)
	UNION ALL
	(SELECT COUNT(car.`owner_id`),owner.`name`,transport.`type` FROM transport,owner,car WHERE transport.type=&#39;car&#39;
	AND owner.`owner_id`=car.`owner_id`
	AND transport.`type_id`=car.`car_id`)  GROUP BY motorbike.owner_id

Can anyone help me please?


Group by with union mysql select query

Please correct me if this question is a duplicate.
Regarding node.js, I&#39;m using socket.io for real-time socket connection from the client application to the server application.
I just heard about engine.io, is engine.io a replacement for socket.io?
I could not find any useful information on engine.io website

Thanks in advance

What&#39;s the difference between engine.io and socket.io?

Can I create a new database simply by connecting to the MongoDB server, or is there another way to create it using Python? If so, how is this done?

How do I create a new database in MongoDB using PyMongo?

<p>Can I create a new database simply by connecting to the MongoDB server, or is there another way to create it using Python? If so, how is this done?</p>


I need to print or convert a float number to 15 decimal place string even if the result has many trailing 0s eg:

1.6 becomes 1.6000000000000000

I tried round(6.2,15) but it returns 6.2000000000000002 adding a rounding error

I also saw various people online who put the float into a string and then added trailing 0&#39;s manually but that seems bad...

What is the best way to do this?

How to print float to n decimal places including trailing 0s?

I have a sample string `&lt;alpha.Customer[cus_Y4o9qMEZAugtnW] active_card=&lt;alpha.AlphaObject[card] ...&gt;, created=1324336085, description=&#39;Customer for My Test App&#39;, livemode=False&gt;`

I only want the value `cus_Y4o9qMEZAugtnW` and NOT `card` (which is inside another `[]`)

How could I do it in easiest possible way in Python?
Maybe by using RegEx (which I am not good at)?


Get the string within brackets in Python

In PHP there a function called [`isset()`](http://php.net/isset) to check if something (like an array index) exists and has a value. How about Python?

I need to use this on arrays because I get &quot;IndexError: list index out of range&quot; sometimes.

I guess I *could* use try/catching, but that&#39;s a last resort.

Check element exists in array

I am sure the configuration of `matplotlib` for python is correct since I have used it to plot some figures.

But today it just stop working for some reason. I tested it with really simple code like:

    import matplotlib.pyplot as plt
    import numpy as np
    x = np.arange(0, 5, 0.1)
    y = np.sin(x)
    plt.plot(x, y)

There&#39;s no error but just no figure shown up. 

I am using python 2.6, Eclipse in Ubuntu
   



How to show matplotlib plots?

I&#39;ve got a following structure:

    |-- dirBar
    |   |-- __init__.py
    |   |-- bar.py
    |-- foo.py
    `-- test.py

bar.py
 
    def returnBar():
        return &#39;Bar&#39;

foo.py

    from dirBar.bar import returnBar

    def printFoo():
        print returnBar()
   
test.py

    from mock import Mock

    from foo import printFoo
    from dirBar import bar

    bar.returnBar = Mock(return_value=&#39;Foo&#39;)

    printFoo()

the result of ``python test.py`` is ``Bar``.

How to mock the ``printBar`` to make it return ``Foo`` so that ``printFoo`` will print it?

EDIT: Without modifying any other file that ``test.py``

How to mock a function defined in a module of a package?

Is there a way to specify a condition of &quot;where document doesn&#39;t contain field&quot; ?

For example, I want to only find the first of these 2 because it doesn&#39;t have the &quot;price&quot; field.

    {&quot;fruit&quot;:&quot;apple&quot;, &quot;color&quot;:&quot;red&quot;}


    {&quot;fruit&quot;:&quot;banana&quot;, &quot;color&quot;:&quot;yellow&quot;, &quot;price&quot;:&quot;2.00&quot;}



MongoDB: Find a document by non-existence of a field?

I&#39;m learning about map-reduce functionality of mongodb. My first tests doesn&#39;t work as I expected and I want to know how is it working.

Is there **any way to write to mongodb console from javascript functions** so I can inspect it?

I tried `console.log(&quot;...&quot;)` but it doesn&#39;t work.

I will ask later about my tests if there isn&#39;t any way to do it.


Is it possible to write to mongodb console in javascript execution?

This is my folder structure:

    +-- express_example
    |---- app.js
    |---- models
    |-------- songs.js
    |-------- albums.js
    |---- and another files of expressjs

My code in file songs.js 

    var mongoose = require(&#39;mongoose&#39;)
    , Schema = mongoose.Schema
    , ObjectId = Schema.ObjectId;

    var SongSchema = new Schema({
	name: {type: String, default: &#39;songname&#39;}
	, link: {type: String, default: &#39;./data/train.mp3&#39;}
	, date: {type: Date, default: Date.now()}
	, position: {type: Number, default: 0}
	, weekOnChart: {type: Number, default: 0}
	, listend: {type: Number, default: 0}
    });

    module.exports = mongoose.model(&#39;Song&#39;, SongSchema);


And here is my code in file albums.js

    var mongoose = require(&#39;mongoose&#39;)
    , Schema = mongoose.Schema
    , ObjectId = Schema.ObjectId;

    var AlbumSchema = new Schema({
	name: {type: String, default: &#39;songname&#39;}
	, thumbnail: {type:String, default: &#39;./images/U1.jpg&#39;}
	, date: {type: Date, default: Date.now()}
	, songs: [SongSchema]
    });

    module.exports = mongoose.model(&#39;Album&#39;, AlbumSchema);

&lt;br/&gt; How can I make albums.js know &lt;strong&gt;SongSchema&lt;/strong&gt; to be defined AlbumSchema

How to get Schema of mongoose database which defined in another model

Is there a dead easy way to rename a collection in mongo?  Something like:

    db.originalCollectionName.rename(&#39;newCollectionName&#39;);

And if not, what is the best way to go about effectively renaming one?

How can I rename a collection in MongoDB?

I know that ObjectIds contain the date they were created on. Is there a way to query this aspect of the ObjectId?


Can I query MongoDB ObjectId by date?

I&#39;m doing a simple insert into Mongo...

    db.notes.insert({ title: &quot;title&quot;, details: &quot;note details&quot;})


After the note document is inserted, I need to get the object id immediately. The result that comes back from the insert has some basic info regarding connection and errors, but no document and field info.

I found some info about using the update() function with upsert=true, I&#39;m just not sure if that&#39;s the right way to go, I have not yet tried it. 




How to get the object id in PyMongo after an insert?

Here is my data structure. 

    [{
    &quot;name&quot;: &quot;David&quot;,
    &quot;lastname&quot;: &quot;&quot;,
    },
    {
    &quot;name&quot;: &quot;Angela&quot;
    }]

&quot;lastname&quot; is sometimes present and sometimes not and sometime is &quot;&quot;.

I want to get all rows that have lastname not equal to &quot;&quot;. But this does not work. It returns both the rows when lastname is &quot;&quot; and when lastname is not present at all. in the example above I want to only get the David node.

    db.collection.find( {&quot;lastname&quot;: {&quot;$ne&quot;: &quot;&quot;}} )



Test empty string in mongodb and pymongo

How to find names of all collections using PyMongo and find all fields in chosen collection ?
I have name of database and name of chosen collection. (Scenario : user input name of database, need to find all collections and show in dropdown list, when user click on one item need to find all fields in that collection)

How to find names of all collections using PyMongo?

With PyMongo, when I try to retrieve objects sorted by their &#39;number&#39; and &#39;date&#39; fields like this:

    db.test.find({&quot;number&quot;: {&quot;$gt&quot;: 1}}).sort({&quot;number&quot;: 1, &quot;date&quot;: -1})

I get this error:

    TypeError: if no direction is specified, key_or_list must be an instance of list

What&#39;s wrong with my sort query?

Using .sort with PyMongo

I&#39;m using pymongo and I can&#39;t figure out how to execute the mongodb interactive shell equivalent of &quot;show dbs&quot;.

Content Type	Original Author	Original Content on Stackoverflow
Question	J.Olufsen	View Question on Stackoverflow
Solution 1 - Python	DarthVader	View Answer on Stackoverflow
Solution 2 - Python	宏杰李	View Answer on Stackoverflow
Solution 3 - Python	Ikar Pohorský	View Answer on Stackoverflow

How do I create a new database in MongoDB using PyMongo?

Python Problem Overview

Python Solutions

Solution 1 - Python

Solution 2 - Python

Solution 3 - Python

What's the difference between engine.io and socket.io?

Group by with union mysql select query

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