Introduction
- Apache CouchDB, commonly referred to as CouchDB, is an open source database that focuses on ease of use and on being "a database that completely embraces the web".
- It is a NoSQL database that uses JSON to store data, JavaScript as its query language using MapReduce and HTTP for an API.
- One of its distinguishing features is multi-master replication.
- Couch is an acronym for cluster of unreliable commodity hardware
- A CouchDB database lacks a schema, or rigid pre-defined data structures such as tables. Data stored in CouchDB is a JSON document(s).
- The structure of the data, or document(s), can change dynamically to accommodate evolving needs.
- CouchDB also offers a built-in administration interface accessible via web called Futon.
Main features
- Document Storage:
- CouchDB stores data as "documents", as one or more field/value pairs expressed as JSON. Field values can be simple things like strings, numbers, or dates; but ordered lists and associative arrays can also be used. Every document in a CouchDB database has a unique id and there is no required document schema.
- ACID Semantics:
- CouchDB provides ACID semantics. It does this by implementing a form of Multi-Version Concurrency Control, meaning that CouchDB can handle a high volume of concurrent readers and writers without conflict.
- Map/Reduce Views and Indexes:
- The stored data is structured using views. In CouchDB, each view is constructed by a JavaScript function that acts as the Map half of a map/reduce operation. The function takes a document and transforms it into a single value which it returns. CouchDB can index views and keep those indexes updated as documents are added, removed, or updated.
- Distributed Architecture with Replication:
- CouchDB was designed with bi-direction replication (or synchronization) and off-line operation in mind. That means multiple replicas can have their own copies of the same data, modify it, and then sync those changes at a later time.
- REST API:
- All items have a unique URI that gets exposed via HTTP. REST uses the HTTP methods POST, GET, PUT and DELETE for the four basic CRUD (Create, Read, Update, Delete) operations on all resources.
- Eventual Consistency:
- CouchDB guarantees eventual consistency to be able to provide both availability and partition tolerance.
- Built for Offline:
- CouchDB can replicate to devices (like smartphones) that can go offline and handle data sync for you when the device is back online.
- Schema-Free:
- Unlike SQL databases, which are designed to store and report on highly structured, interrelated data, CouchDB is designed to store and report on large amounts of semi-structured, document oriented data. CouchDB greatly simplifies the development of document oriented applications, such as collaborative web applications.
- In an SQL database, the schema and storage of the existing data must be updated as needs evolve. With CouchDB, no schema is required, so new document types with new meaning can be safely added alongside the old. However, for applications requiring robust validation of new documents custom validation functions are possible. The view engine is designed to easily handle new document types and disparate but similar documents.
Installation (Ubuntu)
- Open terminal and execute
sudo apt-get install couchdb -y
- If the aptitude/apt-get installation gives an error message then couchdb might not have access to its pid file.
- Fix:
sudo chown -R couchdb /var/run/couchdb
- Need to rerun the setup script:
sudo dpkg --configure couchdb
For Verifying CouchDB, check on Futon: http://127.0.0.1:5984/_utils/index.html
*For installation on other Operating Systems - http://wiki.apache.org/couchdb/Installation
CouchDB Java Client
- Ektorp
- JRelax
- jcouchdb
- DroidCouch
- CouchDB4J
- LightCouch
CouchDB4J Example
- CouchDB4J is an updated Java library for CouchDB.
- It handles the REST style calls to the CouchDB server behind the scenes, and give you a handle on the JSON objects directly.
- CouchDB4J uses JSON-lib to handle mapping to/from JSON objects, which makes getting/setting properties on the objects very easy.
- You can even map Java objects to JSON objects and back to make the process easier.
- Example:
Structure:
CouchDBCompleteDemo.java
package com.couchdb.demo;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.List;
import java.util.Map;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.simple.JSONValue;
import com.fourspaces.couchdb.Database;
import com.fourspaces.couchdb.Document;
import com.fourspaces.couchdb.Session;
import com.fourspaces.couchdb.ViewResults;
public class CouchDBCompleteDemo {
static Session dbSession ;
static Database db;
public static void main(String[] args) {
String dbName = "foodb";
createDatabase(dbName);
saveDocument(getDocument("1", "Willian", "J2EECOE", "TL", "Android"));
saveDocument(getDocument("2", "Joanne", "J2EECOE", "Developer", "Java"));
saveDocument(getDocument("3", "suzzane", "J2EECOE", "Sr. Developer", "Java"));
saveDocument(getDocument("4", "Harley", "J2EECOE", "Sr. Developer", "Java"));
saveDocument(getDocument("5", "Julian", "J2EECOE", "Developer", "Java"));
saveDocument(getDocument("6", "Peter", "J2EECOE", "Developer", "Java"));
getTotalDocumentCount();
viewAllDocuments();
viewsDemo();
// deleteDocument("6");
// getTotalDocumentCount();
// deleteDatabase(dbName);
}
public static void createDatabase(String dbName){
dbSession = new Session("localhost", 5984);
db = dbSession.createDatabase(dbName);
if(db==null)
db = dbSession.getDatabase(dbName);
}
public static Document getDocument(String id,String name,String group,String designation,String language){
Document doc = new Document();
doc.setId(id);
doc.put("EmpNO", id);
doc.put("Name", name);
doc.put("Group", group);
doc.put("Designation", designation);
doc.put("Language", language);
return doc;
}
public static void saveDocument(Document doc){
try {
db.saveDocument(doc);
} catch (Exception e) {
}
}
public static int getTotalDocumentCount(){
int count = db.getDocumentCount();
System.out.println("Total Documents: " + count);
return count;
}
public static void deleteDocument(String id){
Document d = db.getDocument(id);
System.out.println("Document 1: " + d);
db.deleteDocument(d);
}
public static void deleteDatabase(String dbName){
dbSession.deleteDatabase(dbName);
}
public static void viewAllDocuments(){
ViewResults results = db.getAllDocuments();
List<Document> documentsList = results.getResults();
if(documentsList!=null)
{
for(Document doc : documentsList)
{
System.out.println(doc.get("id") + " : " + doc);
}
}
}
public static void viewsDemo(){
if(db!=null)
{
Document doc = null;
try {
doc = db.getDocument("_design/couchview");
} catch (Exception e1) {
doc = null;
}
try {
if(doc==null)
{
doc = new Document();
doc.setId("_design/couchview");
String str = "{\"javalanguage\": {\"map\": \"function(doc) { if (doc.Language == 'Java') emit(null, doc) } \"}, \"java_and_se\": {\"map\": \"function(doc) { if (doc.Language == 'Java' & doc.Designation == 'SE') emit(null, doc) } \"}}";
doc.put("views", str);
db.saveDocument(doc);
}
} catch (Exception e) {
}
}
try {
DefaultHttpClient httpclient = new DefaultHttpClient();
HttpGet get = new HttpGet("http://localhost:5984/foodb/_design/couchview/_view/javalanguage");
HttpResponse response = httpclient.execute(get);
HttpEntity entity=response.getEntity();
InputStream instream = entity.getContent();
BufferedReader reader = new BufferedReader(new InputStreamReader(instream));
String strdata = null;
String jsonString = "" ;
while( (strdata =reader.readLine())!=null)
{
// System.out.println(strdata);
jsonString += strdata;
}
System.out.println("Json String: " + jsonString);
Map<String, Object> jsonMap = getMapFromJsonString(jsonString);
if(jsonMap!=null)
{
System.out.println("total_rows: " + jsonMap.get("total_rows"));
System.out.println("offset: " + jsonMap.get("offset"));
List<Map> rowsList = (List<Map>) jsonMap.get("rows");
if(rowsList!=null)
{
for(Map row: rowsList)
{
System.out.println("----------------");
System.out.println("Id: " + row.get("id"));
System.out.println("Value: " + row.get("value"));
System.out.println("Name: " + ((Map)row.get("value")).get("Name"));
System.out.println("_id: " + ((Map)row.get("value")).get("_id"));
System.out.println("Language: " + ((Map)row.get("value")).get("Language"));
System.out.println("EmpNO: " + ((Map)row.get("value")).get("EmpNO"));
System.out.println("Designation: " + ((Map)row.get("value")).get("Designation"));
System.out.println("Group: " + ((Map)row.get("value")).get("Group"));
}
}
}
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IllegalStateException e) {
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public static Map<String, Object> getMapFromJsonString(String jsonString){
Map<String, Object> jsonMap = (Map<String, Object>) JSONValue.parse(jsonString);
System.out.println("Json Map: " + jsonMap);
return jsonMap;
}
}
