nGQL风格指南Graph

nGQL没有严格的构建格式要求，但根据恰当而统一的风格创建nGQL语句有利于提高可读性、避免歧义。在同一组织或项目中使用相同的nGQL风格有利于降低维护成本，规避因格式混乱或误解造成的问题。本文为写作nGQL语句提供了风格参考。

换行Graph

1. 换行写子句。

   不推荐：

   GO FROM "player100" OVER follow REVERSELY YIELD src(edge) AS id;
   

   推荐：

   GO FROM "player100" \
   OVER follow REVERSELY \
   YIELD src(edge) AS id;
   

2. 换行写复合语句中的不同语句。

   不推荐：

   GO FROM "player100" OVER follow REVERSELY YIELD src(edge) AS id | GO FROM $-.id \
   OVER serve WHERE properties($^).age > 20 YIELD properties($^).name AS FriendOf, properties($$).name AS Team;
   

   推荐：

   GO FROM "player100" \
   OVER follow REVERSELY \
   YIELD src(edge) AS id | \
   GO FROM $-.id OVER serve \
   WHERE properties($^).age > 20 \
   YIELD properties($^).name AS FriendOf, properties($$).name AS Team;
   

3. 子句长度超过80个字符时，在合适的位置换行。

   不推荐：

   MATCH (v:player{name:"Tim Duncan"})-[e]->(v2) \
   WHERE (v2.name STARTS WITH "Y" AND v2.age > 35 AND v2.age < v.age) OR (v2.name STARTS WITH "T" AND v2.age < 45 AND v2.age > v.age) \
   RETURN v2;
   

   推荐：

   MATCH (v:player{name:"Tim Duncan"})-[e]->(v2) \
   WHERE (v2.name STARTS WITH "Y" AND v2.age > 35 AND v2.age < v.age) \
   OR (v2.name STARTS WITH "T" AND v2.age < 45 AND v2.age > v.age) \
   RETURN v2;
   

标识符命名Graph

在nGQL语句中，关键字、标点符号、空格以外的字符内容都是标识符。推荐的标识符命名方式如下。

1. 使用单数名词命名Tag，用原型动词或动词短语构成Edge type。

   不推荐：

   MATCH p=(v:players)-[e:are_following]-(v2) \
   RETURN nodes(p);
   

   推荐：

   MATCH p=(v:player)-[e:follow]-(v2) \
   RETURN nodes(p);
   

2. 标识符用蛇形命名法，以下划线（_）连接单词，且所有字母小写。

   不推荐：

   MATCH (v:basketballTeam) \
   RETURN v;
   

   推荐：

   MATCH (v:basketball_team) \
   RETURN v;
   

3. 语法关键词大写，变量小写。

   不推荐：

   go from "player100" over Follow
   

   推荐:

   GO FROM "player100" OVER follow
   

PatternGraph

1. 分行写Pattern时，在表示边的箭头右侧换行，而不是左侧。

   不推荐：

   MATCH (v:player{name: "Tim Duncan", age: 42}) \
   -[e:follow]->()-[e:serve]->()<--(v3) \
   RETURN v, e, v2;
   

   推荐：

   MATCH (v:player{name: "Tim Duncan", age: 42})-[e:follow]-> \
   ()-[e:serve]->()<--(v3) \
   RETURN v, e, v2;
   

2. 将无需查询的点和边匿名化。

   不推荐：

   MATCH (v:player)-[e:follow]->(v2) \
   RETURN v;
   

   推荐：

   MATCH (v:player)-[:follow]->() \
   RETURN v;
   

3. 将非匿名点放在匿名点的前面。

   不推荐：

   MATCH ()-[:follow]->(v) \
   RETURN v;
   

   推荐：

   MATCH (v)<-[:follow]-() \
   RETURN v;
   

字符串Graph

字符串用双引号包围。

不推荐：

RETURN 'Hello Nebula!';

推荐：

RETURN "Hello Nebula!\"123\"";

RETURN "\"NebulaGraph is amazing,\" the user says.";

结束语句Graph

1. 用英文分号（;）结束nGQL语句。

   不推荐：

   FETCH PROP ON player "player100"
   

   推荐：

   FETCH PROP ON player "player100";
   

2. 使用管道符（|）分隔的复合语句，仅在最后一行末用英文分号结尾。在管道符前使用英文分号会导致语句执行失败。

   不支持：

   GO FROM "player100" \
   OVER follow \
   YIELD dst(edge) AS id; | \
   GO FROM $-.id \
   OVER serve \
   YIELD properties($$).name AS Team, properties($^).name AS Player;
   

   支持：

   GO FROM "player100" \
   OVER follow \
   YIELD dst(edge) AS id | \
   GO FROM $-.id \
   OVER serve \
   YIELD properties($$).name AS Team, properties($^).name AS Player;
   

3. 在包含自定义变量的复合语句中，用英文分号结束定义变量的语句。不按规则加分号或使用管道符结束该语句会导致执行失败。

   不支持：

   $var = GO FROM "player100" \
   OVER follow \
   YIELD dst(edge) AS id \
   GO FROM $var.id \
   OVER serve \
   YIELD properties($$).name AS Team, properties($^).name AS Player;
   

   也不支持：

   $var = GO FROM "player100" \
   OVER follow \
   YIELD dst(edge) AS id | \
   GO FROM $var.id \
   OVER serve \
   YIELD properties($$).name AS Team, properties($^).name AS Player;
   

   支持：

   $var = GO FROM "player100" \
   OVER follow \
   YIELD dst(edge) AS id; \
   GO FROM $var.id \
   OVER serve \
   YIELD properties($$).name AS Team, properties($^).name AS Player;