From SQL to Cypher
package cn.dh.neo; import java.io.File; import java.io.IOException; import java.util.HashMap; import java.util.Iterator; import java.util.Map; import org.neo4j.cypher.javacompat.ExecutionEngine; import org.neo4j.cypher.javacompat.ExecutionResult; import org.neo4j.graphdb.GraphDatabaseService; import org.neo4j.graphdb.Node; import org.neo4j.graphdb.RelationshipType; import org.neo4j.graphdb.Transaction; import org.neo4j.graphdb.factory.GraphDatabaseFactory; import org.neo4j.graphdb.index.Index; import org.neo4j.kernel.impl.util.FileUtils; /** * * <p>User: 裴东辉 * <p>Date: 2014-8-6 上午10:43:10 * <p>Version: 1.0 */ public class Neosql { public static enum RelationshipTypes implements RelationshipType { FLLOW, //用户链 歌手出版专辑 EMAIL//用户-邮箱 专辑包含很多歌曲 } public final String USERPK="name"; public final String EMAILPK="email"; /** * 数据初始化 * @author 裴东辉 * @since 2014-8-6 上午10:46:18 */ public void initdata(){ try {FileUtils.deleteRecursively(new File("db/user.db"));} catch (IOException e) {e.printStackTrace();} //删除数据库 GraphDatabaseService graphDb = new GraphDatabaseFactory().newEmbeddedDatabase( "db/user.db" ); try(Transaction tx = graphDb.beginTx()){ //节点索引 Index<Node> usersIndex = graphDb.index().forNodes("usersIndex"); //-----------------第1个用户,第1个用户的2个邮箱 Node node1 = graphDb.createNode(); node1.setProperty(USERPK, "admin"); usersIndex.add(node1, USERPK, node1.getProperty(USERPK)); Node node1_1=graphDb.createNode(); node1_1.setProperty(EMAILPK, "[email protected]"); node1_1.setProperty("comment", "work"); usersIndex.add(node1_1, EMAILPK, node1_1.getProperty(EMAILPK)); Node node1_2=graphDb.createNode(); node1_2.setProperty(EMAILPK, "[email protected]"); node1_2.setProperty("comment", "home"); usersIndex.add(node1_2, EMAILPK, node1_2.getProperty(EMAILPK)); node1.createRelationshipTo(node1_1, RelationshipTypes.EMAIL); node1.createRelationshipTo(node1_2, RelationshipTypes.EMAIL); //-----------------第2个用户,第2个用户的2个邮箱 Node node2 = graphDb.createNode(); node2.setProperty(USERPK, "user"); usersIndex.add(node2, USERPK, node2.getProperty(USERPK)); Node node2_1=graphDb.createNode(); node2_1.setProperty(EMAILPK, "[email protected]"); node2_1.setProperty("comment", "work"); usersIndex.add(node2_1, EMAILPK, node2_1.getProperty(EMAILPK)); Node node2_2=graphDb.createNode(); node2_2.setProperty(EMAILPK, "[email protected]"); node2_2.setProperty("comment", "home"); usersIndex.add(node2_2, EMAILPK, node2_2.getProperty(EMAILPK)); node2.createRelationshipTo(node2_1, RelationshipTypes.EMAIL); node2.createRelationshipTo(node2_2, RelationshipTypes.EMAIL); //----两个用户之间的关联关系 node1.createRelationshipTo(node2, RelationshipTypes.FLLOW); tx.success(); }finally{ graphDb.shutdown(); } } /** * select * from t_user where name = ‘admin‘ * start user=node:usersIndex(name = {name} ) return user ,其中的{name}通过一个Map的参数传递过去params * 1、SQL starts with the result you want — we SELECT what we want and then declare how to source it. In Cypher, the START clause is quite a different concept which specifies starting points in the graph from which the query will execute. 2、From a SQL point of view, the identifiers in START are like table names that point to a set of nodes or relationships. The set can be listed literally, come via parameters, or as I show in the following example, be defined by an index look-up. 3、So in fact rather than being SELECT-like, the START clause is somewhere between the FROM and the WHERE clause in SQL. * @author 裴东辉 * @since 2014-8-6 上午11:08:44 */ public void findUserByName(String name){ GraphDatabaseService graphDb = new GraphDatabaseFactory().newEmbeddedDatabase( "db/user.db" ); try(Transaction tx = graphDb.beginTx()){ ExecutionEngine engine = new ExecutionEngine(graphDb); Map<String, Object> params = new HashMap<String, Object>(); params.put("name",name); ExecutionResult result = engine.execute( "start user=node:usersIndex(name = {name} ) return user",params); Iterator<Node> nodeIta=result.columnAs("user"); Node node=null; while(nodeIta.hasNext()){ node=nodeIta.next(); infoln(node+"-"+node.getProperty(USERPK)); } tx.success(); }finally{ graphDb.shutdown(); } } /** * 1、select t_email.* from t_user join t_email on t_user.id = t_email.user_id where t_user.name = ‘admin‘ 2、start user=node:usersIndex(name = {name}) match user-[:EMAIL]->email return email 3、Unlike SQL which operates on sets, Cypher predominantly works on sub-graphs. The relational equivalent is the current set of tuples being evaluated during a SELECT query. 4、The shape of the sub-graph is specified in the MATCH clause. The MATCH clause is analogous to the JOIN in SQL. A normal a→b relationship is an inner join between nodes a and b both sides have to have at least one match, or nothing is returned. 5、We’ll start with a simple example, where we find all email addresses that are connected to the person “admin”. This is an ordinary one-to-many relationship. 6、There is no join table here, but if one is necessary the next example will show how to do that, writing the pattern relationship like so: -[r:belongs_to]-> will introduce (the equivalent of) join table available asthe variable r. In reality this is a named relationship in Cypher, so we’re saying “join Person to Group viabelongs_to.” To illustrate this, consider this image, comparing the SQL model and Neo4j/Cypher. * @author 裴东辉 * @since 2014-8-6 上午11:40:10 */ public void findEmailByUserName(String name){ GraphDatabaseService graphDb = new GraphDatabaseFactory().newEmbeddedDatabase( "db/user.db" ); try(Transaction tx = graphDb.beginTx()){ ExecutionEngine engine = new ExecutionEngine(graphDb); Map<String, Object> params = new HashMap<String, Object>(); params.put("name", name); ExecutionResult result = engine.execute( "start user=node:usersIndex(name = {name}) match user-[:EMAIL]->email return email",params); Iterator<Node> nodeIta=result.columnAs("email"); Node node=null; while(nodeIta.hasNext()){ node=nodeIta.next(); infoln(node+"-"+node.getProperty(EMAILPK)); } tx.success(); }finally{ graphDb.shutdown(); } } public void info(Object j){System.out.print(j.toString());} public void infoln(Object j){System.out.println(j.toString());} /** * @author 裴东辉 * @since 2014-8-6 上午10:42:54 * @param args */ public static void main(String[] args) { new Neosql().initdata(); new Neosql().findUserByName("user"); new Neosql().findEmailByUserName("admin"); } }
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