A MongoDB instance is running in MongoDB.

There is no way in the world, and when there are more people, the road will become. Why can't I create a MongoDB on ipvs?

After taking a series of actions in NoSQL, The Postgres community is not waiting. Postgres has been making progress: Integrating JSON and PLV8. PLV8 into the V8 Javascript Engine. JSON operations are simpler (verification required ).

Preparations before you start:

• Postgres 9.2 + (as of this blog entry, 9.2 is in beta)-http://www.postgresql.org/ftp/source/

• V8 https://github.com/v8/v8

• PLV8 http://code.google.com/p/plv8js/wiki/PLV8

The minimum level of MongoDB is set. The set can be expressed in tables:

Create table some_collection (
Some_collection_id serial not null primary key,
Data JSON
);

JSON of the struct type is saved in the s table, which is easy to use (as shown in the following figure ).

The following describes how to automatically create a set and save it in the set table:

Create table collection (
Collection_id serial not null primary key,
Name VARCHAR
);

-- Make sure the name is unique
Create unique index idx_collection_constraint ON collection (name );

Once the table is created, you can use the stored procedure to automatically create a set. The method is to create a table first and then insert the sequence of table creation.

Create or replace function create_collection (collection varchar) RETURNS
Boolean AS $
Var plan1 = plv8.prepare ('insert INTO collection (name) VALUES ($1) ', ['varchar']);
Var plan2 = plv8.prepare ('create TABLE col _ '+ collection +
'(Col _' + collection + '_ id int not null primary key, data JSON )');
Var plan3 = plv8.prepare ('create SEQUENCE seq_col _ '+ collection );

Var ret;

Try {
Plv8.subtransaction (function (){
Plan1.execute ([collection]);
Plan2.execute ([]);
Plan3.execute ([]);

Ret = true;
});
} Catch (err ){
Ret = false;
}

Plan1.free ();
Plan2.free ();
Plan3.free ();

Return ret;
$ LANGUAGE plv8 immutable strict;

With the stored procedure, it is much easier:

SELECT create_collection ('My _ collect ');

To solve the problem of centralized storage, let's take a look at MongoDB data parsing. MongoDB completes this operation through the point annotation method:

Create or replace function find_in_obj (data json, key varchar) RETURNS
Varchar as $
Var obj = JSON. parse (data );
Var parts = key. split ('.');

Var part = parts. shift ();
While (part & (obj = obj [part])! = Undefined ){
Part = parts. shift ();
}

// This will either be the value, or undefined
Return obj;
$ LANGUAGE plv8 STRICT;

The above function returns VARCHAR and does not apply to all cases, but it is useful for strings:

SELECT data
FROM col_my_collection
WHERE find_in_obj (data, 'some. element') = 'something cool'

In addition to string comparison, MongoDB also provides comparison of numeric types and the keyword exists. Below are different implementations of the find_in_obj () method:

Create or replace function find_in_obj_int (data json, key varchar) RETURNS
Int as $
Var obj = JSON. parse (data );
Var parts = key. split ('.');

Var part = parts. shift ();
While (part & (obj = obj [part])! = Undefined ){
Part = parts. shift ();
}

Return Number (obj );
$ LANGUAGE plv8 STRICT;

Create or replace function find_in_obj_exists (data json, key varchar) RETURNS
Boolean as $
Var obj = JSON. parse (data );
Var parts = key. split ('.');

Var part = parts. shift ();
While (part & (obj = obj [part])! = Undefined ){
Part = parts. shift ();
}

Return (obj = undefined? 'F': 'T ');
$ LANGUAGE plv8 STRICT;

The next step is data query. Use existing materials to implement the find () method.

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MongoDB beginners must read (both concepts and practices)

MongoDB authoritative Guide (The Definitive Guide) in English [PDF]

 

For more details, please continue to read the highlights on the next page:

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