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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。

Compatibility

nGQL 风格与Graph不同。

换行Graph

  1. 换行写子句。

    不推荐：

    GO FROM "player100" OVER follow REVERSELY YIELD follow._dst AS id;

    推荐：

    GO FROM "player100" \
OVER follow REVERSELY \
YIELD follow._dst 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 follow._dst AS id | GO FROM $-.id \
OVER serve WHERE $^.player.age > 20 YIELD $^.player.name AS FriendOf, $$.team.name AS Team;

    推荐：

    GO FROM "player100" \
OVER follow REVERSELY \
YIELD follow._dst AS id | \
GO FROM $-.id OVER serve \
WHERE $^.player.age > 20 \
YIELD $^.player.name AS FriendOf, $$.team.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;

Note

即使子句不超过80个字符，如需换行后有助于理解，也可将子句再次分行。

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\"";

Note

字符串中需要嵌套单引号或双引号时，用反斜线（\）转义。例如:

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 follow._dst AS id; | \
GO FROM $-.id \
OVER serve \
YIELD $$.team.name AS Team, $^.player.name AS Player;

    支持：

    GO FROM "player100" \
OVER follow \
YIELD follow._dst AS id | \
GO FROM $-.id \
OVER serve \
YIELD $$.team.name AS Team, $^.player.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 follow._dst AS id \
GO FROM $var.id \
OVER serve \
YIELD $$.team.name AS Team, $^.player.name AS Player;

    也不支持：

    $var = GO FROM "player100" \
OVER follow \
YIELD follow._dst AS id | \
GO FROM $var.id \
OVER serve \
YIELD $$.team.name AS Team, $^.player.name AS Player;

    支持：

    $var = GO FROM "player100" \
OVER follow \
YIELD follow._dst AS id; \
GO FROM $var.id \
OVER serve \
YIELD $$.team.name AS Team, $^.player.name AS Player;
最后更新: September 14, 2021
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