`mongorestore` will only drop the existing collection if you use the `--drop` argument.

If you don&#39;t use `--drop`, all documents will be inserted into the existing collection, unless a document with the same `_id` already exists. Documents with the same `_id` will be skipped, they are not merged. So `mongorestore` will never delete or modify any of the existing data by default.

Ok, I think I might be overlooking something obvious/simple here... but I need to write a query that returns only records that match multiple criteria on the same column...

My table is a very simple linking setup for applying flags to a user ...

    ID   contactid  flag        flag_type 
    -----------------------------------
    118  99         Volunteer   1 
    119  99         Uploaded    2 
    120  100        Via Import  3 
    121  100        Volunteer   1  
    122  100        Uploaded    2

etc... in this case you&#39;ll see both contact 99 and 100 are flagged as both &quot;Volunteer&quot; and &quot;Uploaded&quot;...

What I need to be able to do is return those contactid&#39;s ONLY that match multiple criteria entered via a search form...the contactid&#39;s have to match ALL chosen flags... in my head the SQL should look something like:

    SELECT contactid 
     WHERE flag = &#39;Volunteer&#39; 
       AND flag = &#39;Uploaded&#39;...

but... that returns nothing... What am I doing wrong here?

SELECTING with multiple WHERE conditions on same column

I wish to hold a heap of objects, not just numbers.  They will have an integer attribute in them that the heap can sort by.  The easiest way to use heaps in python is heapq, but how do I tell it to sort by a specific attribute when using heapq?

How to make heapq evaluate the heap off of a specific attribute?

I need to import (restore) a collection generated with `mongodump` into an existing database and I&#39;d like the records to be merged into the existing collection.

Does `mongorestore` merge the records in the same collection or it will drop the existing collection before restoring the records?

MongoDB mongorestore and existing collection with records

<p>I need to import (restore) a collection generated with <code>mongodump</code> into an existing database and I'd like the records to be merged into the existing collection.</p>
<p>Does <code>mongorestore</code> merge the records in the same collection or it will drop the existing collection before restoring the records?</p>


I would like to execute a following query:
 
    db.mycollection.find(HAS IMAGE URL)

What should be the correct syntax?

How do you query for &quot;is not null&quot; in Mongo?

In MongoDB, if I were to store an array (say `[&quot;red&quot;, &quot;blue&quot;]`) in a field `&quot;color&quot;`, does it index `&quot;red&quot;` and `&quot;blue&quot;` so I could query for `&quot;red&quot;`, for example, or does in make `{&quot;red&quot;, &quot;blue&quot;}` a composite index?

How does MongoDB index arrays?

I&#39;m sure MongoDB doesn&#39;t officially support &quot;joins&quot;. What does this mean?

Does this mean &quot;We cannot connect two collections(tables) together.&quot;?

I think if we put the value for `_id` in collection A to the `other_id` in collection B, can we simply connect two collections?

If my understanding is correct, MongoDB can connect two tables together, say, when we run a query. This is done by &quot;Reference&quot; written in &lt;http://www.mongodb.org/display/DOCS/Schema+Design&gt;.

Then what does &quot;joins&quot; really mean?

I&#39;d love to know the answer because this is essential to learn MongoDB schema design. &lt;http://www.mongodb.org/display/DOCS/Schema+Design&gt;

MongoDB and &quot;joins&quot;

I know that `MongoDB` accepts and retrieves records as JSON/BSON objects, but how does it actually store these files on disk? Are they stored as a collection of individual `*.json` files or as one large file? I have a hunch as to the latter, since the `MongoDB` docs state that it works best on systems with `ext4/xfs`, which are better at handling large files. Can anyone confirm?

How is the data in a MongoDB database stored on disk?

Can you share your thoughts how would you implement data versioning in MongoDB. (I&#39;ve asked [similar question regarding Cassandra][1]. If you have any thoughts which db is better for that please share)

Suppose that I need to version records in an simple address book. (Address book records are stored as flat json objects). I expect that the history:

- will be used infrequently
- will be used all at once to present it in a &quot;time machine&quot; fashion
- there won&#39;t be more versions than few hundred to a single record.
history won&#39;t expire.

I&#39;m considering the following approaches:

- Create a new object collection to store history of records or changes to the records. It would store one object per version with a reference to the address book entry. Such records would looks as follows:

    &lt;pre&gt;
    {
     &#39;_id&#39;: &#39;new id&#39;,
     &#39;user&#39;: user_id,
     &#39;timestamp&#39;: timestamp,
     &#39;address_book_id&#39;: &#39;id of the address book record&#39; 
     &#39;old_record&#39;: {&#39;first_name&#39;: &#39;Jon&#39;, &#39;last_name&#39;:&#39;Doe&#39; ...}
    }
    &lt;/pre&gt;
    This approach can be modified to store an array of versions per document. But this seems to be slower approach without any advantages.

- Store versions as serialized (JSON) object attached to address book entries. I&#39;m not sure how to attach such objects to MongoDB documents. Perhaps as an array of strings.
([Modelled after Simple Document Versioning with CouchDB][2])


  [1]: https://stackoverflow.com/questions/4183945/ways-to-implement-data-versioning-in-cassandra
  [2]: http://blog.couchone.com/post/632718824/simple-document-versioning-with-couchdb

Ways to implement data versioning in MongoDB

I have used `mongodump` to dump my database of mongodb, it created some bson files under `dump/mydb`

But I don&#39;t know how to use them. I tried `mongoimport`, but seems it can&#39;t import bson data. Then how to use these bson files? How to import them to another mongodb?

How to use the dumped data by mongodump?

I want to load data/restore dump data in mongoDB using mongorestore. I am trying to command

    mongorestore dump

but it giving me error 

    Sat Sep 21 16:12:33.403 JavaScript execution failed: SyntaxError: Unexpected identifier


How can we restore or put data into mongoDB?? Please give me the steps. 

How to restore the dump into your running mongodb

I created a dump with mongodump on computer A (ubuntu 12.04 server). I moved it to computer B (ubuntu 12.04 server) and typed:

&gt; mongorestore -db db_name --drop db_dump_path

It failed and it reported:

&gt; connected to: 127.0.0.1&lt;br&gt;
&gt; terminate called after throwing an instance of &#39;std::runtime_error&#39;&lt;br&gt;
&gt; what():  locale::facet::_S_create_c_locale name not valid&lt;br&gt;
&gt; Aborted

I&#39;ve successfully accomplished this operation before and this strange behavior has never occurred. What do I need to do to fix this?

MongoDB mongorestore failure: locale::facet::_S_create_c_locale name not valid

In MongoDB, is it possible to dump a database and restore the content to a different database? For example like this:

    mongodump --db db1 --out dumpdir
    mongorestore --db db2 --dir dumpdir

But it doesn&#39;t work. Here&#39;s the error message:

&gt;   building a list of collections to restore from dumpdir dir
&gt;
&gt;   don&#39;t know what to do with subdirectory &quot;dumpdir/db1&quot;, skipping...
&gt;
&gt;   done


Content Type	Original Author	Original Content on Stackoverflow
Question	Simone Carletti	View Question on Stackoverflow
Solution 1 - Mongodb	Niels van der Rest	View Answer on Stackoverflow

MongoDB mongorestore and existing collection with records

Mongodb Problem Overview

Mongodb Solutions

Solution 1 - Mongodb

How to make heapq evaluate the heap off of a specific attribute?

SELECTING with multiple WHERE conditions on same column

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