Gremlin - 如果顶点不存在,则仅添加顶点 [英] Gremlin - only add a vertex if it doesn't exist
问题描述
我有一组用户名(例如 ['abc','def','ghi']
)要添加到图表中的用户"标签下.
I have an array of usernames (eg. ['abc','def','ghi']
) to be added under 'user' label in the graph.
现在我首先要检查用户名是否已经存在 (gV().hasLabel('user').has('username','def')
) 然后只添加那些'user' 标签下的 username 属性不匹配.
Now I first want to check if the username already exists (g.V().hasLabel('user').has('username','def')
) and then add only those for which the username property doesn't match under 'user' label.
此外,这可以在单个 gremlin 查询或 groovy 脚本中完成吗?
Also, can this be done in a single gremlin query or groovy script?
我正在使用 Titan 图数据库、tinkerpop3 和 gremlin REST 服务器.
I am using titan graph database, tinkerpop3 and gremlin REST server.
推荐答案
使用脚本",您始终可以将多行/命令脚本传递给服务器进行处理,以完成您想要完成的任务.然后通过使用变量、if/then 语句等的普通编程技术回答这个问题:
With "scripts" you can always pass a multi-line/command script to the server for processing to get what you want done. This question is then answered with normal programming techniques using variables, if/then statements, etc:
t = g.V().has('person','name','bill')
t.hasNext() ? t.next() : g.addV('person').property('name','bill').next()
或者也许:
g.V().has('person','name','bill').tryNext().orElseGet{
g.addV('person').property('name','bill').next()}
但这些都是 groovy 脚本,最终 TinkerPop 建议避免使用脚本和闭包,以支持纯遍历.在单次遍历中处理获取或创建"的一般方法是做这样的事情:
But these are groovy scripts and ultimately TinkerPop recommends avoiding scripts and closures in favor of a pure traversal. The general way to handle a "get or create" in a single traversal is to do something like this:
gremlin> g.V().has('person','name','bill').fold().
......1> coalesce(unfold(),
......2> addV('person').property('name','bill'))
==>v[18]
另请参阅此StackOverflow 问题,了解有关 upsert/获取或创建"模式的更多信息.
Also see this StackOverflow question for more information on upsert/"get or create" patterns.
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