Discuss Neo4j ”; Previous Next Neo4j is one of the popular Graph Databases and Cypher Query Language (CQL). Neo4j is written in Java Language. This tutorial explains the basics of Neo4j, Java with Neo4j, and Spring DATA with Neo4j. The tutorial is divided into sections such as Neo4j Introduction, Neo4j CQL, Neo4j CQL Functions, Neo4j Admin, etc. Each of these sections contain related topics with simple and useful examples. Print Page Previous Next Advertisements ”;
Neo4j – Quick Guide ”; Previous Next Neo4j – Overview Neo4j is the world”s leading open source Graph Database which is developed using Java technology. It is highly scalable and schema free (NoSQL). What is a Graph Database? A graph is a pictorial representation of a set of objects where some pairs of objects are connected by links. It is composed of two elements – nodes (vertices) and relationships (edges). Graph database is a database used to model the data in the form of graph. In here, the nodes of a graph depict the entities while the relationships depict the association of these nodes. Popular Graph Databases Neo4j is a popular Graph Database. Other Graph Databases are Oracle NoSQL Database, OrientDB, HypherGraphDB, GraphBase, InfiniteGraph, and AllegroGraph. Why Graph Databases? Nowadays, most of the data exists in the form of the relationship between different objects and more often, the relationship between the data is more valuable than the data itself. Relational databases store highly structured data which have several records storing the same type of data so they can be used to store structured data and, they do not store the relationships between the data. Unlike other databases, graph databases store relationships and connections as first-class entities. The data model for graph databases is simpler compared to other databases and, they can be used with OLTP systems. They provide features like transactional integrity and operational availability. RDBMS Vs Graph Database Following is the table which compares Relational databases and Graph databases. Sr.No RDBMS Graph Database 1 Tables Graphs 2 Rows Nodes 3 Columns and Data Properties and its values 4 Constraints Relationships 5 Joins Traversal Advantages of Neo4j Following are the advantages of Neo4j. Flexible data model − Neo4j provides a flexible simple and yet powerful data model, which can be easily changed according to the applications and industries. Real-time insights − Neo4j provides results based on real-time data. High availability − Neo4j is highly available for large enterprise real-time applications with transactional guarantees. Connected and semi structures data − Using Neo4j, you can easily represent connected and semi-structured data. Easy retrieval − Using Neo4j, you can not only represent but also easily retrieve (traverse/navigate) connected data faster when compared to other databases. Cypher query language − Neo4j provides a declarative query language to represent the graph visually, using an ascii-art syntax. The commands of this language are in human readable format and very easy to learn. No joins − Using Neo4j, it does NOT require complex joins to retrieve connected/related data as it is very easy to retrieve its adjacent node or relationship details without joins or indexes. Features of Neo4j Following are the notable features of Neo4j − Data model (flexible schema) − Neo4j follows a data model named native property graph model. Here, the graph contains nodes (entities) and these nodes are connected with each other (depicted by relationships). Nodes and relationships store data in key-value pairs known as properties. In Neo4j, there is no need to follow a fixed schema. You can add or remove properties as per requirement. It also provides schema constraints. ACID properties − Neo4j supports full ACID (Atomicity, Consistency, Isolation, and Durability) rules. Scalability and reliability − You can scale the database by increasing the number of reads/writes, and the volume without effecting the query processing speed and data integrity. Neo4j also provides support for replication for data safety and reliability. Cypher Query Language − Neo4j provides a powerful declarative query language known as Cypher. It uses ASCII-art for depicting graphs. Cypher is easy to learn and can be used to create and retrieve relations between data without using the complex queries like Joins. Built-in web application − Neo4j provides a built-in Neo4j Browser web application. Using this, you can create and query your graph data. Drivers − Neo4j can work with − REST API to work with programming languages such as Java, Spring, Scala etc. Java Script to work with UI MVC frameworks such as Node JS. It supports two kinds of Java API: Cypher API and Native Java API to develop Java applications. In addition to these, you can also work with other databases such as MongoDB, Cassandra, etc. Indexing − Neo4j supports Indexes by using Apache Lucence. Neo4j – Data Model Neo4j Property Graph Data Model Neo4j Graph Database follows the Property Graph Model to store and manage its data. Following are the key features of Property Graph Model − The model represents data in Nodes, Relationships and Properties Properties are key-value pairs Nodes are represented using circle and Relationships are represented using arrow keys Relationships have directions: Unidirectional and Bidirectional Each Relationship contains “Start Node” or “From Node” and “To Node” or “End Node” Both Nodes and Relationships contain properties Relationships connects nodes In Property Graph Data Model, relationships should be directional. If we try to create relationships without direction, then it will throw an error message. In Neo4j too, relationships should be directional. If we try to create relationships without direction, then Neo4j will throw an error message saying that “Relationships should be directional”. Neo4j Graph Database stores all of its data in Nodes and Relationships. We neither need any additional RRBMS Database nor any SQL database to store Neo4j database data. It stores its data in terms of Graphs in its native format. Neo4j uses Native GPE (Graph Processing Engine) to work with its Native graph storage format. The main building blocks of Graph DB Data Model are − Nodes Relationships Properties Following is a simple example of a Property Graph. Here, we have represented Nodes using Circles. Relationships are represented using Arrows. Relationships are directional. We can represent Node”s data in terms of Properties (key-value pairs). In this example, we have represented each Node”s Id property within the Node”s Circle. Neo4j – Environment Setup In this chapter, we will discuss how to install Neo4j in your system using exe file. Neo4j Database Server Setup with Windows exe File Follow the steps given
Neo4j – Count Function ”; Previous Next Assume we have created a graph in the database with the following details. Count The count() function is used to count the number of rows. Syntax Following is the syntax of the count function. MATCH (n { name: ”A” })–>(x) RETURN n, count(*) Example Following is a sample Cypher Query which demonstrates the usage of the count() function. Match(n{name: “India”, result: “Winners”})–(x) RETURN n, count(*) To execute the above query, carry out the following steps − Step 1 − Open the Neo4j desktop App and start the Neo4j Server. Open the built-in browser app of Neo4j using the URL http://localhost:7474/ as shown in the following screenshot. Step 2 − Copy and paste the desired query in the dollar prompt and press the play button (to execute the query) highlighted in the following screenshot. Result On executing, you will get the following result. Group Count The COUNT clause is also used to count the groups of relationship types. Example Following is a sample Cypher Query which counts and returns the number of nodes participating in each relation. Match(n{name: “India”, result: “Winners”})-[r]-(x) RETURN type (r), count(*) To execute the above query, carry out the following steps − Step 1 − Open the Neo4j desktop App and start the Neo4j Server. Open the built-in browser app of Neo4j using the URL http://localhost:7474/ as shown in the following screenshot. Step 2 − Copy and paste the desired query in the dollar prompt and press the play button (to execute the query) highlighted in the following screenshot. Result On executing, you will get the following result. Print Page Previous Next Advertisements ”;
Neo4j – Index ”; Previous Next Neo4j SQL supports Indexes on node or relationship properties to improve the performance of the application. We can create indexes on properties for all nodes, which have the same label name. We can use these indexed columns on MATCH or WHERE or IN operator to improve the execution of CQL command. In this chapter, we will discuss how to − Create an Index Delete an Index Creating an Index Neo4j CQL provides “CREATE INDEX” command to create indexes on Node or Relationship properties. Syntax Following is the syntax to create an index in Neo4j. CREATE INDEX ON:label (node) Example Before proceeding with the example, create a node Dhawan as shown below. CREATE (Dhawan:player{name: “shikar Dhawan”, YOB: 1995, POB: “Delhi”}) Following is a sample Cypher Query to create an index on the node Dhawan in Neo4j. CREATE INDEX ON:player(Dhawan) To execute the above query, carry out the following steps − Step 1 − Open the Neo4j desktop App and start the Neo4j Server. Open the built-in browser app of Neo4j using the URL http://localhost:7474/ as shown below. Step 2 − Copy and paste the desired query in the dollar prompt and press the play button (to execute the query) highlighted in the following screenshot. Result On executing, you will get the following result. Deleting an Index Neo4j CQL provides a “DROP INDEX” command to drop an existing index of a Node or Relationshis property. Syntax Following is the syntax to create an index in Neo4j. DROP INDEX ON:label(node) Example Following is a sample Cypher Query to create an index on the node named “Dhawan” in Neo4j. DROP INDEX ON:player(Dhawan) To execute the above query, carry out the following steps − Step 1 − Open the Neo4j desktop App and start the Neo4j Server. Open the built-in browser app of Neo4j using the URL http://localhost:7474/ as shown in the following screenshot. Step 2 − Copy and paste the desired query in the dollar prompt and press the play button (to execute the query) highlighted in the following screenshot. Result On executing, you will get the following result. Print Page Previous Next Advertisements ”;
Neo4j – Drop Unique ”; Previous Next We have already discussed creating UNIQUE constraint operations with examples in the previous chapter. In this chapter, we will discuss dropping UNIQUE constraint operation with examples. Neo4j CQL provides “DROP CONSTRAINT” command to delete existing Unique constraint from a node or relationship property. Syntax Following is the syntax for dropping a UNIQUE constraint in Neo4j. DROP CONSTRAINT ON (node:label) ASSERT node.id IS UNIQUE Example Following is a sample Cypher Query to remove the UNIQUE constraint on the property id. DROP CONSTRAINT ON (n:player) ASSERT n.id IS UNIQUE To execute the above query, carry out the following steps − Step 1 − Open the Neo4j desktop App and start the Neo4j Server. Open the built-in browser app of Neo4j using the URL http://localhost:7474/ as shown in the following screenshot. Step 2 − Copy and paste the desired query in the dollar prompt and press the play button (to execute the query) highlighted in the following screenshot. Result On executing, you will get the following result. Print Page Previous Next Advertisements ”;
Neo4j – Create Unique Constraint ”; Previous Next In Neo4j database, CQL CREATE command always creates a new node or relationship which means even though you use the same values, it inserts a new row. As per our application requirements for some nodes or relationships, we have to avoid this duplication. For this, we should use some database constraints to create a rule on one or more properties of a node or relationship. Like SQL, Neo4j database also supports UNIQUE constraint on node or relationship properties. UNIQUE constraint is used to avoid duplicate records and to enforce data integrity rule. Create UNIQUE Constraint Neo4j CQL provides “CREATE CONSTRAINT” command to create unique constraints on node or relationship properties. Syntax Following is the syntax to create a UNIQUE constraint in Neo4j. MATCH (root {name: “Dhawan”}) CREATE UNIQUE (root)-[:LOVES]-(someone) RETURN someone Example Before proceeding with the example, create 4 nodes as shown below. CREATE(Dhawan:player{id:001, name: “shikar Dhawan”, YOB: 1995, POB: “Delhi”}) CREATE(Jonathan:player {id:002, name: “Jonathan Trott”, YOB: 1981, POB: “CapeTown”}) CREATE(Sangakkara:player {id:003, name: “Kumar Sangakkara”, YOB: 1977, POB: “Matale”}) CREATE(Rohit:player {id:004, name: “Rohit Sharma”, YOB: 1987, POB: “Nagpur”}) CREATE(Virat:player {id:005, name: “Virat Kohli”, YOB: 1988, POB: “Delhi”}) Following is a sample Cypher Query to create a UNIQUE constraint on the property id using Neo4j. CREATE CONSTRAINT ON (n:player) ASSERT n.id IS UNIQUE To execute the above query, carry out the following steps − Step 1 − Open the Neo4j desktop App and start the Neo4j Server. Open the built-in browser app of Neo4j using the URL http://localhost:7474/ as shown in the following screenshot. Step 2 − Copy and paste the desired query in the dollar prompt and press the play button (to execute the query) highlighted in the following screenshot. Result On executing, you will get the following result. Verification Now, try to add another node with a redundant id value. Here, we are trying to create a node with id 002. CREATE (Jadeja:player {id:002, name: “Ravindra Jadeja”, YOB: 1988, POB: “NavagamGhed”}) If you execute this query, you will get an error message as shown in the following screenshot. Print Page Previous Next Advertisements ”;
Neo4j – Useful Resources ”; Previous Next The following resources contain additional information on Neo4j. Please use them to get more in-depth knowledge on this. Print Page Previous Next Advertisements ”;
Neo4j – With Clause ”; Previous Next You can chain the query arts together using the WITH clause. Syntax Following is the syntax of the WITH clause. MATCH (n) WITH n ORDER BY n.property RETURN collect(n.property) Example Following is a sample Cypher Query which demonstrates the usage of the WITH clause. MATCH (n) WITH n ORDER BY n.name DESC LIMIT 3 RETURN collect(n.name) To execute the above query, carry out the following steps − Step 1 − Open the Neo4j desktop App and start the Neo4j Server. Open the built-in browser app of Neo4j using the URL http://localhost:7474/ as shown in the following screenshot. Step 2 − Copy and paste the desired query in the dollar prompt and press the play button (to execute the query) highlighted in the following screenshot. Result On executing, you will get the following result. Print Page Previous Next Advertisements ”;
Neo4j – Unwind Clause ”; Previous Next The unwind clause is used to unwind a list into a sequence of rows. Example Following is a sample Cypher Query which unwinds a list. UNWIND [a, b, c, d] AS x RETURN x To execute the above query, carry out the following steps − Step 1 − Open the Neo4j desktop App and start the Neo4j Server. Open the built-in browser app of Neo4j using the URL http://localhost:7474/ as shown in the following screenshot. Step 2 − Copy and paste the desired query in the dollar prompt and press the play button (to execute the query) highlighted in the following screenshot. Result On executing, you will get the following result. Print Page Previous Next Advertisements ”;
Neo4j – Backup & Restore ”; Previous Next In real-time applications, we should take backup of our application database regularly, so that we can restore to some working condition at any failure point. This rule is applicable for both RDBMS and NoSQL databases. In this section, we are going to discuss about two important DBA tasks. How to back up a Neo4j Database. How to restore Neo4j Database to a specific backup. Note − These steps are applicable to Windows Operating System only. We should use similar kind of commands to do the same steps in other operating systems. Neo4j Database Backup Step 1 − Click “Neo4j Community” using the following path − Windows “Start” button → “All Programs” → “Neo4j Community” → “Neo4j Community” By default, it selects c:Users[username]DocumentsNeo4jdefault.graphdb. However if we wish to, we can change the path to a different directory. Step 2 − Here we have changed to our Neo4j Database folder. C:Ne04j2.0db Step 3 − Click the “Start” button. Once the server starts, we can observe our Neo4j Database files are generated at a specified directory. Before taking a database backup, the first and foremost thing we should do is shutdown the Neo4j Database server. Step 4 − Click the “Stop” button to shut down the server. Neo4j Database files are available at C:Ne04j2.0db Step 5 − Open the command prompt. Step 6 − Create a folder “Neo4jDbBackup-01” at C:Neo4j (This may be any location in your file system). mkdir C:Neo4jNeo4jDbBackup-01 It creates a new folder “Neo4jDbBackup-01” at the specified file system location “C:Neo4j” Step 7 − Type the following command and press Enter key. copy C:Ne04j2.0db C:Neo4jNeo4jDbBackup-01 This means our files are copied to the required destination folder. Access that folder and observe that the folder has our database files. Step 8 − Use any Windows compression/decompression tool like WinZip, 7 Zip, or WinRAR to zip our Database folder. Step 9 − Now our Neo4jDbBackup-01.zip file is created. If you have any memory constraints in your file system, then remove “Neo4jDbBackup-01” folder at “C:Neo4j” Neo4j Database Restore Step 1 − Shutdown the database server. Please refer to the previous steps to shut down the server. Step 2 − Empty the current database folder. Step 3 − Use any Windows compression/decompression tool like WinZip, 7 Zip, or WinRar to unzip our backup folder. Step 4 − Open the command prompt and execute the following command. Copy C:Neo4jNeo4jDbBackup-01 C:Ne04j2.0db Now we can observe that our database folder contains working backup files Step 5 − Start the server by clicking the “Start” button. Step 6 − Execute some MATCH + RETURN commands to verify whether we have restored our database properly. Print Page Previous Next Advertisements ”;