MongoDB Java API

Address: http://keben1983.blog.163.com/blog/static/143638081201010591157929/

This document is translated from the [Java language center] section of the document mongodb-docs-2010-10-24.pdf, which is compiled according to your own understanding.

I hope to give some help and memo to my friends who have started to contact me like this, because I just learned that many of these functions are currently unavailable. In the future, I am not sure what functions are available, you can also directly view this document.

MongoDB Java driver for simple operations

I. Java driver consistency

MongoDB Java drivers are thread-safe. For general applications, only one Mongo instance is required. Mongo has a built-in connection pool (the pool size is 10 by default ).

In an environment with a large number of writes and reads, we can use the following methods to ensure consistency when the same dB is used in a session:

Db mdb = Mongo. getdb ('dbname ');

MDB. requeststart ();
//
// Business Code
//
MDB. requestdone ();

DB and dbcollection are absolutely thread-safe, and they are cached, so the same object may be obtained in the application.

2. Save/find an object (dbobject)

The Java Driver provides the dbobject interface to save objects to the database.

Define the object to be saved:

Public class tweet implements dbobject {
/**......*/
}

Then we can use this object:

Tweet tweet = new tweet ();
Tweet. Put ("user", userid );
Tweet. Put ("message", message );
Tweet. Put ("date", new date ());

Collection. insert (Tweet );

When querying from a database, the results are automatically converted to dbobject objects. We can convert them to our own types:

Collection. setobjectclass (Tweet );

Tweet mytweet = (Tweet) collection. findone ();

3. Create a connection

Mongo M = new Mongo ();
Mongo M = new Mongo ("localhost ");
Mongo M = new Mongo ("localhost", 27017 );

DB = M. getdb ("mydb );

Note: In fact, a mongo instance represents a database connection pool. Even in a multi-threaded environment, a mongo instance is sufficient for us.

Iv. Authentication (optional)

Boolean auth = dB. Authenticate ("myusername", "mypasswd ");

5. Retrieve collection list

Set <string> colls = dB. getcollectionnames ();

For (string S: colls ){
System. Out. prinln (s );
}

6. Get a collection

Dbcollection coll = dB. getcollection ("testcollection ");

Using dbcollection, We can insert and query data.

VII. Insert a document

Suppose there is a JSON document as follows:

{
"Name": "MongoDB ",
"Type": "Database ",
"Count": 1,
"Info ":{
X: 203,
Y: 102
}
}

Note: The preceding JSON document has an embedded document "info ".

We can use basicdbobject to create a document that is the same as the preceding JSON and save it in MongoDB.

Dbobject Doc = new basicdbobject ();

Doc. Put ("name", "MongoDB ");
Doc. Put ("type", "Database ");
Doc. Put ("count", 1 );

Dbobject info = new basicdbobject ();
Info. Put ("X", 203 );
Info. Put ("Y", 102 );

Doc. Put ("info", Info );

Coll. insert (DOC );

8. query the first document (findone ())

To verify the JSON-like data stored above, we can use the findone () method to obtain the data.

Findone (): returns a document;
Find (): returns a cursor (dbcursor) that contains a group of objects dbobject;

Dbobject Doc = Coll. findone ();
System. Out. println (DOC );

We will see the console output:
{"_ Id": "49902cde5162504500b45c2c", "name": "MongoDB", "type": "Database", "Count": 1, "info ": {"X": 203, "Y": 102}, "_ ns": "testcollection "}

IX. Insert multiple documents

To show more query methods later, we first insert several documents whose JSON files are as follows:
{
"I": Value
}

Insert data in a loop:

For (INT I = 0; I <100; I ++ ){
Coll. insert (New basicdbobject (). append ("I", I ));
}

We have noticed that we can insert data of different styles in the same Coll, which is an important feature of MongoDB: "Free mode ".

10. Number of statistical documents

Now we have 101 documents in the database, and check whether the statistics are correct.

Long Count = Coll. getcount ();
System. Out. println (count );

The console will output 101

11. Use a cursor to retrieve all documents

Dbcursor cursor = Coll. Find ();

While (cursor. hasnext ()){
Dbobject object = cursor. Next ();
System. Out. println (object );
}

12. query a single document

Dbobject query = new basicdbobject ();

Query. Put ("I", 71 );

Cursor = Coll. Find (query );

While (cur. hasnext ()){
Dbobject object = cursor. Next ();
System. Out. println (object );
}

The console output is similar to the following:

{"_ Id": "49903677516250c1008d624e", "I": 71, "_ ns": "testcollection "}

13. query the document set

Based on the query conditions, we can use dbcollection to retrieve multiple objects from the database, such as querying the document set of I> 50:

Query = new basicdbobject ();

Query. Put ("I", new basicdbobject ("$ gt", 50); // I> 50

Cursor = Coll. Find (query );

While (cursor. hasnext ()){
Dbobject object = cursor. Next ();
System. Out. println (object );
}

For example, the query condition is 20 <I <= 30:

Query = new basicdbobject ();

// 20 <I <= 30
Query. Put ("I", new basicdbobject ("$ gt", 20). append ("$ LTE", 30 ));

Cursor = Coll. Find (query );

While (cursor. hasnext ()){
Dbobject object = cursor. Next ();
System. Out. println (object );
}

14. Create an index

MongoDB supports indexing, and it is very easy to add an index to a dbcollection. You only need to specify the fields to create the index, and then specify whether it is in ascending or descending order (-1, for example, create an index in ascending order on "I.

Coll. createindex (New basicdbobject ("I", 1); // 1 indicates Ascending Order

15. query Indexes

We can query all the indexes:

List <dbobject> List = Coll. getindexinfo ();

For (dbobject index: List ){
System. Out. println (INDEX );
}

The console output is similar to the following:

{"Name": "I _1", "ns": "mydb. testcollection "," key ": {" I ": 1}," _ ns ":" system. indexes "}

MongoDB Management Function

1. Obtain all databases

Mongo M = new Mongo ();

For (string S: M. getdatabasenames ()){
System. Out. println (s );
}

Ii. delete a database

M. dropdatabase ("my_new_db ");

Java type of MongoDB

1. Object ID

Objectid is used as the unique ID automatically generated.

Objectid id = new objectid ();
Objectid copy = new objectid (ID );

Ii. Regular Expressions

Pattern John = pattern. Compile ("Joh? N ", case_insensitive );
Dbobject query = new basicdbobject ("name", John );

// Query all "name" matches/Joh? N/I documentation
Dbcursor cursor = collection. Find (query );

Iii. Date and Time

Date Now = new date ();
Dbobject time = new basicdbobject ("ts", now );

Collection. Save (time );

Iv. Database reference

Dbref can be used to save database references.

Dbref addressref = new dbref (dB, "foo. Bar", address_id );
Dbobject address = addressref. Fetch ();

Dbobject person = basicdbobjectbuilder. Start ()
. Add ("name", "Fred ")
. Add ("Address", addressref)
. Get ();
Collection. Save (person );

Dbobject Fred = collection. findone ();
Dbref addressobj = (dbref) Fred. Get ("Address ");
Addressobj. Fetch ();

V. binary data

Byte array (byte []) is treated as binary data.

Vi. embedded documents

JSON data is as follows:
{
"X ":{
"Y": 3
}
}

In MongoDB, Java indicates:

Dbobject y = new basicdbobject ("Y", 3 );
Dbobject x = new basicdbobject ("X", y );

VII. Array

Any object inherited from list is considered as an array in MongoDB.

If you want to represent the following JSON data:

{
"X ":[
1,
2,
{"Foo": "bar "},
4
]
}

In Java, it should be:

List <Object> X = new arraylist <Object> ();
X. Add (1 );
X. Add (2 );
X. Add (New basicdbobject ("foo", "bar "));
X. Add (4 );

Dbobject Doc = new basicdbobject ("X", X );
System. Out. println (DOC );