Neo4j3.5学习笔记——图算法Graph Algorithm Examples

跟着官网代码学习.jpg–jdk 1.8.0 & neo4j 3.5
https://neo4j.com/docs/java-reference/current/java-embedded/

目标：得到A和 B两个节点之间的最短路径

• 由于我尚未掌握junit，因此上传至github上的代码与官网的代码不尽相同。

1. 创建一个图数据库：
1）通过创建T类型为PropertyContainer的子类来设置setProperties方法，使得createNode方法能够实现("property类型”，“对应具体值”，"property类型”，“对应具体值”，…)的方式创建Node。

private Node createNode(final Object... properties) {
    return setProperties(graphDb.createNode(), properties);}
private <T extends PropertyContainer> T setProperties(final T entity, final Object[] properties) {
    for(int i = 0; i < properties.length; i++) {
    String key = properties[i++].toString();Object value = properties[i];entity.setProperty(key, value);}return entity;}

2) 建立Node以及Node之间的Relationship。

Node nodeA = createNode( "name", "A", "x", 0d, "y", 0d );
Node nodeB = createNode( "name", "B", "x", 7d, "y", 0d );
Node nodeC = createNode( "name", "C", "x", 2d, "y", 1d );
Relationship relAB = createRelationship( nodeA, nodeC, "length", 2d );
Relationship relBC = createRelationship( nodeC, nodeB, "length", 3d );
Relationship relAC = createRelationship( nodeA, nodeB, "length", 10d );private Relationship createRelationship(final Node start, final Node end, final Object... properties) {
    return setProperties(start.createRelationshipTo(end, RelType.MY_TYPE), properties);}

2. 计算最短路径：
1) 使用Dijkstra方法计算最短路径：

public WeightedPath findCheapestPathWithDijkstra(final Node nodeA, final Node nodeB) {
    PathFinder<WeightedPath> finder = GraphAlgoFactory.dijkstra(PathExpanders.forTypeAndDirection(RelType.MY_TYPE, Direction.BOTH), "length");WeightedPath path = finder.findSinglePath(nodeA, nodeB);path.weight();return path;
}

2) 使用aStar方法计算你最短路径：

EstimateEvaluator<Double> estimateEvaluator = new EstimateEvaluator<Double>(){
    @Overridepublic Double getCost( final Node node, final Node goal ){
    double dx = (Double) node.getProperty( "x" ) - (Double) goal.getProperty( "x" );double dy = (Double) node.getProperty( "y" ) - (Double) goal.getProperty( "y" );double result = Math.sqrt( Math.pow( dx, 2 ) + Math.pow( dy, 2 ) );return result;}};PathFinder<WeightedPath> astar = GraphAlgoFactory.aStar(PathExpanders.allTypesAndDirections(),CommonEvaluators.doubleCostEvaluator( "length" ), estimateEvaluator );WeightedPath path = astar.findSinglePath( nodeA, nodeB );