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QUERY LANGUAGE

1: HugeGraph Gremlin
2: HugeGraph Examples

1 - HugeGraph Gremlin

概述

HugeGraph支持Apache TinkerPop3的图形遍历查询语言Gremlin。 SQL是关系型数据库查询语言，而Gremlin是一种通用的图数据库查询语言，Gremlin可用于创建图的实体（Vertex和Edge）、修改实体内部属性、删除实体，也可执行图的查询操作。

Gremlin可用于创建图的实体（Vertex和Edge）、修改实体内部属性、删除实体，更主要的是可用于执行图的查询及分析操作。

TinkerPop Features

HugeGraph实现了TinkerPop框架，但是并没有实现TinkerPop所有的特性。

下表列出HugeGraph对TinkerPop各种特性的支持情况：

Graph Features

Name	Description	Support
Computer	Determines if the {@code Graph} implementation supports {@link GraphComputer} based processing	false
Transactions	Determines if the {@code Graph} implementations supports transactions.	true
Persistence	Determines if the {@code Graph} implementation supports persisting it’s contents natively to disk.This feature does not refer to every graph’s ability to write to disk via the Gremlin IO packages(.e.g. GraphML), unless the graph natively persists to disk via those options somehow. For example,TinkerGraph does not support this feature as it is a pure in-sideEffects graph.	true
ThreadedTransactions	Determines if the {@code Graph} implementation supports threaded transactions which allow a transaction be executed across multiple threads via {@link Transaction#createThreadedTx()}.	false
ConcurrentAccess	Determines if the {@code Graph} implementation supports more than one connection to the same instance at the same time. For example, Neo4j embedded does not support this feature because concurrent access to the same database files by multiple instances is not possible. However, Neo4j HA could support this feature as each new {@code Graph} instance coordinates with the Neo4j cluster allowing multiple instances to operate on the same database.	false

Vertex Features

Name	Description	Support
UserSuppliedIds	Determines if an {@link Element} can have a user defined identifier. Implementation that do not support this feature will be expected to auto-generate unique identifiers. In other words, if the {@link Graph} allows {@code graph.addVertex(id,x)} to work and thus set the identifier of the newly added {@link Vertex} to the value of {@code x} then this feature should return true. In this case, {@code x} is assumed to be an identifier data type that the {@link Graph} will accept.	false
NumericIds	Determines if an {@link Element} has numeric identifiers as their internal representation. In other words,if the value returned from {@link Element#id()} is a numeric value then this method should be return {@code true}. Note that this feature is most generally used for determining the appropriate tests to execute in the Gremlin Test Suite.	false
StringIds	Determines if an {@link Element} has string identifiers as their internal representation. In other words, if the value returned from {@link Element#id()} is a string value then this method should be return {@code true}. Note that this feature is most generally used for determining the appropriate tests to execute in the Gremlin Test Suite.	false
UuidIds	Determines if an {@link Element} has UUID identifiers as their internal representation. In other words,if the value returned from {@link Element#id()} is a {@link UUID} value then this method should be return {@code true}.Note that this feature is most generally used for determining the appropriate tests to execute in the Gremlin Test Suite.	false
CustomIds	Determines if an {@link Element} has a specific custom object as their internal representation.In other words, if the value returned from {@link Element#id()} is a type defined by the graph implementations, such as OrientDB’s {@code Rid}, then this method should be return {@code true}.Note that this feature is most generally used for determining the appropriate tests to execute in the Gremlin Test Suite.	false
AnyIds	Determines if an {@link Element} any Java object is a suitable identifier. TinkerGraph is a good example of a {@link Graph} that can support this feature, as it can use any {@link Object} as a value for the identifier. Note that this feature is most generally used for determining the appropriate tests to execute in the Gremlin Test Suite. This setting should only return {@code true} if {@link #supportsUserSuppliedIds()} is {@code true}.	false
AddProperty	Determines if an {@link Element} allows properties to be added. This feature is set independently from supporting “data types” and refers to support of calls to {@link Element#property(String, Object)}.	true
RemoveProperty	Determines if an {@link Element} allows properties to be removed.	true
AddVertices	Determines if a {@link Vertex} can be added to the {@code Graph}.	true
MultiProperties	Determines if a {@link Vertex} can support multiple properties with the same key.	false
DuplicateMultiProperties	Determines if a {@link Vertex} can support non-unique values on the same key. For this value to be {@code true}, then {@link #supportsMetaProperties()} must also return true. By default this method, just returns what {@link #supportsMultiProperties()} returns.	false
MetaProperties	Determines if a {@link Vertex} can support properties on vertex properties. It is assumed that a graph will support all the same data types for meta-properties that are supported for regular properties.	false
RemoveVertices	Determines if a {@link Vertex} can be removed from the {@code Graph}.	true

Edge Features

Name	Description	Support
UserSuppliedIds	Determines if an {@link Element} can have a user defined identifier. Implementation that do not support this feature will be expected to auto-generate unique identifiers. In other words, if the {@link Graph} allows {@code graph.addVertex(id,x)} to work and thus set the identifier of the newly added {@link Vertex} to the value of {@code x} then this feature should return true. In this case, {@code x} is assumed to be an identifier data type that the {@link Graph} will accept.	false
NumericIds	Determines if an {@link Element} has numeric identifiers as their internal representation. In other words,if the value returned from {@link Element#id()} is a numeric value then this method should be return {@code true}. Note that this feature is most generally used for determining the appropriate tests to execute in the Gremlin Test Suite.	false
StringIds	Determines if an {@link Element} has string identifiers as their internal representation. In other words, if the value returned from {@link Element#id()} is a string value then this method should be return {@code true}. Note that this feature is most generally used for determining the appropriate tests to execute in the Gremlin Test Suite.	false
UuidIds	Determines if an {@link Element} has UUID identifiers as their internal representation. In other words,if the value returned from {@link Element#id()} is a {@link UUID} value then this method should be return {@code true}.Note that this feature is most generally used for determining the appropriate tests to execute in the Gremlin Test Suite.	false
CustomIds	Determines if an {@link Element} has a specific custom object as their internal representation.In other words, if the value returned from {@link Element#id()} is a type defined by the graph implementations, such as OrientDB’s {@code Rid}, then this method should be return {@code true}.Note that this feature is most generally used for determining the appropriate tests to execute in the Gremlin Test Suite.	false
AnyIds	Determines if an {@link Element} any Java object is a suitable identifier. TinkerGraph is a good example of a {@link Graph} that can support this feature, as it can use any {@link Object} as a value for the identifier. Note that this feature is most generally used for determining the appropriate tests to execute in the Gremlin Test Suite. This setting should only return {@code true} if {@link #supportsUserSuppliedIds()} is {@code true}.	false
AddProperty	Determines if an {@link Element} allows properties to be added. This feature is set independently from supporting “data types” and refers to support of calls to {@link Element#property(String, Object)}.	true
RemoveProperty	Determines if an {@link Element} allows properties to be removed.	true
AddEdges	Determines if an {@link Edge} can be added to a {@code Vertex}.	true
RemoveEdges	Determines if an {@link Edge} can be removed from a {@code Vertex}.	true

Data Type Features

Name	Description	Support
BooleanValues		true
ByteValues		true
DoubleValues		true
FloatValues		true
IntegerValues		true
LongValues		true
MapValues	Supports setting of a {@code Map} value. The assumption is that the {@code Map} can contain arbitrary serializable values that may or may not be defined as a feature itself	false
MixedListValues	Supports setting of a {@code List} value. The assumption is that the {@code List} can contain arbitrary serializable values that may or may not be defined as a feature itself. As this{@code List} is “mixed” it does not need to contain objects of the same type.	false
BooleanArrayValues		false
ByteArrayValues		true
DoubleArrayValues		false
FloatArrayValues		false
IntegerArrayValues		false
LongArrayValues		false
SerializableValues		false
StringArrayValues		false
StringValues		true
UniformListValues	Supports setting of a {@code List} value. The assumption is that the {@code List} can contain arbitrary serializable values that may or may not be defined as a feature itself. As this{@code List} is “uniform” it must contain objects of the same type.	false

Gremlin的步骤

HugeGraph支持Gremlin的所有步骤。有关Gremlin的完整参考信息，请参与Gremlin官网。

步骤	说明	文档
addE	在两个顶点之间添加边	addE step
addV	将顶点添加到图形	addV step
and	确保所有遍历都返回值	and step
as	用于向步骤的输出分配变量的步骤调制器	as step
by	与`group`和`order`配合使用的步骤调制器	by step
coalesce	返回第一个返回结果的遍历	coalesce step
constant	返回常量值。与`coalesce`配合使用	constant step
count	从遍历返回计数	count step
dedup	返回已删除重复内容的值	dedup step
drop	丢弃值（顶点/边缘）	drop step
fold	充当用于计算结果聚合值的屏障	fold step
group	根据指定的标签将值分组	group step
has	用于筛选属性、顶点和边缘。支持`hasLabel`、`hasId`、`hasNot` 和 `has` 变体	has step
inject	将值注入流中	inject step
is	用于通过布尔表达式执行筛选器	is step
limit	用于限制遍历中的项数	limit step
local	本地包装遍历的某个部分，类似于子查询	local step
not	用于生成筛选器的求反结果	not step
optional	如果生成了某个结果，则返回指定遍历的结果，否则返回调用元素	optional step
or	确保至少有一个遍历会返回值	or step
order	按指定的排序顺序返回结果	order step
path	返回遍历的完整路径	path step
project	将属性投影为映射	project step
properties	返回指定标签的属性	properties step
range	根据指定的值范围进行筛选	range step
repeat	将步骤重复指定的次数。用于循环	repeat step
sample	用于对遍历返回的结果采样	sample step
select	用于投影遍历返回的结果	select step
store	用于遍历返回的非阻塞聚合	store step
tree	将顶点中的路径聚合到树中	tree step
unfold	将迭代器作为步骤展开	unfold step
union	合并多个遍历返回的结果	union step
V	包括顶点与边之间的遍历所需的步骤：`V`、`E`、`out`、`in`、`both`、`outE`、`inE`、`bothE`、`outV`、`inV`、`bothV` 和 `otherV`	order step
where	用于筛选遍历返回的结果。支持 `eq`、`neq`、`lt`、`lte`、`gt`、`gte` 和 `between` 运算符	where step

2 - HugeGraph Examples

1 概述

本示例将TitanDB Getting Started 为模板来演示HugeGraph的使用方法。通过对比HugeGraph和TitanDB，了解HugeGraph和TitanDB的差异。

1.1 HugeGraph与TitanDB的异同

HugeGraph和TitanDB都是基于Apache TinkerPop3框架的图数据库，均支持Gremlin图查询语言，在使用方法和接口方面具有很多相似的地方。然而HugeGraph是全新设计开发的，其代码结构清晰，功能较为丰富，接口更为友好等特点。

HugeGraph相对于TitanDB而言，其主要特点如下：

HugeGraph目前有HugeGraph-API、HugeGraph-Client、HugeGraph-Loader、HugeGraph-Studio、HugeGraph-Spark等完善的工具组件，可以完成系统集成、数据载入、图可视化查询、Spark 连接等功能；
HugeGraph具有Server和Client的概念，第三方系统可以通过jar引用、client、api等多种方式接入，而TitanDB仅支持jar引用方式接入。
HugeGraph的Schema需要显式定义，所有的插入和查询均需要通过严格的schema校验，目前暂不支持schema的隐式创建。
HugeGraph充分利用后端存储系统的特点来实现数据高效存取，而TitanDB以统一的Kv结构无视后端的差异性。
HugeGraph的更新操作可以实现按需操作（例如：更新某个属性）性能更好。TitanDB的更新是read and update方式。
HugeGraph的VertexId和EdgeId均支持拼接，可实现自动去重，同时查询性能更好。TitanDB的所有Id均是自动生成，查询需要经索引。

1.2 人物关系图谱

本示例通过Property Graph Model图数据模型来描述希腊神话中各人物角色的关系（也被成为人物关系图谱），具体关系详见下图。

其中，圆形节点代表实体(Vertex)，箭头代表关系（Edge），方框的内容为属性。

该关系图谱中有两类顶点，分别是人物（character）和位置（location）如下表：

名称	类型	属性
character	vertex	name,age,type
location	vertex	name

有六种关系，分别是父子（father）、母子（mother）、兄弟（brother）、战斗（battled）、居住(lives)、拥有宠物（pet）关于关系图谱的具体信息如下：

名称	类型	source vertex label	target vertex label	属性
father	edge	character	character	-
mother	edge	character	character	-
brother	edge	character	character	-
pet	edge	character	character	-
lives	edge	character	location	reason

在HugeGraph中，每个edge label只能作用于一对source vertex label和target vertex label。也就是说，如果一个图内定义了一种关系father连接character和character，那farther就不能再连接其他的vertex labels。

因此本例子将原TitanDB中的monster, god, human, demigod均使用相同的vertex label: character来表示, 同时增加属性type来标识人物的类型。edge label与原TitanDB保持一致。当然为了满足edge label约束，也可以通过调整edge label的name来实现。

2 Graph Schema and Data Ingest Examples

HugeGraph需要显示创建Schema，因此需要依次创建PropertyKey、VertexLabel、EdgeLabel，如果有需要索引还需要创建IndexLabel。

2.1 Graph Schema

schema = hugegraph.schema()

schema.propertyKey("name").asText().ifNotExist().create()
schema.propertyKey("age").asInt().ifNotExist().create()
schema.propertyKey("time").asInt().ifNotExist().create()
schema.propertyKey("reason").asText().ifNotExist().create()
schema.propertyKey("type").asText().ifNotExist().create()

schema.vertexLabel("character").properties("name", "age", "type").primaryKeys("name").nullableKeys("age").ifNotExist().create()
schema.vertexLabel("location").properties("name").primaryKeys("name").ifNotExist().create()

schema.edgeLabel("father").link("character", "character").ifNotExist().create()
schema.edgeLabel("mother").link("character", "character").ifNotExist().create()
schema.edgeLabel("battled").link("character", "character").properties("time").ifNotExist().create()
schema.edgeLabel("lives").link("character", "location").properties("reason").nullableKeys("reason").ifNotExist().create()
schema.edgeLabel("pet").link("character", "character").ifNotExist().create()
schema.edgeLabel("brother").link("character", "character").ifNotExist().create()

2.2 Graph Data

// add vertices
Vertex saturn = graph.addVertex(T.label, "character", "name", "saturn", "age", 10000, "type", "titan")
Vertex sky = graph.addVertex(T.label, "location", "name", "sky")
Vertex sea = graph.addVertex(T.label, "location", "name", "sea")
Vertex jupiter = graph.addVertex(T.label, "character", "name", "jupiter", "age", 5000, "type", "god")
Vertex neptune = graph.addVertex(T.label, "character", "name", "neptune", "age", 4500, "type", "god")
Vertex hercules = graph.addVertex(T.label, "character", "name", "hercules", "age", 30, "type", "demigod")
Vertex alcmene = graph.addVertex(T.label, "character", "name", "alcmene", "age", 45, "type", "human")
Vertex pluto = graph.addVertex(T.label, "character", "name", "pluto", "age", 4000, "type", "god")
Vertex nemean = graph.addVertex(T.label, "character", "name", "nemean", "type", "monster")
Vertex hydra = graph.addVertex(T.label, "character", "name", "hydra", "type", "monster")
Vertex cerberus = graph.addVertex(T.label, "character", "name", "cerberus", "type", "monster")
Vertex tartarus = graph.addVertex(T.label, "location", "name", "tartarus")

// add edges
jupiter.addEdge("father", saturn)
jupiter.addEdge("lives", sky, "reason", "loves fresh breezes")
jupiter.addEdge("brother", neptune)
jupiter.addEdge("brother", pluto)
neptune.addEdge("lives", sea, "reason", "loves waves")
neptune.addEdge("brother", jupiter)
neptune.addEdge("brother", pluto)
hercules.addEdge("father", jupiter)
hercules.addEdge("mother", alcmene)
hercules.addEdge("battled", nemean, "time", 1)
hercules.addEdge("battled", hydra, "time", 2)
hercules.addEdge("battled", cerberus, "time", 12)
pluto.addEdge("brother", jupiter)
pluto.addEdge("brother", neptune)
pluto.addEdge("lives", tartarus, "reason", "no fear of death")
pluto.addEdge("pet", cerberus)
cerberus.addEdge("lives", tartarus)

2.3 Indices

HugeGraph默认是自动生成Id，如果用户通过primaryKeys指定VertexLabel的primaryKeys字段列表后，VertexLabel的Id策略将会自动切换到primaryKeys策略。启用primaryKeys策略后,HugeGraph通过vertexLabel+primaryKeys拼接生成VertexId ，可实现自动去重，同时无需额外创建索引即可以使用primaryKeys中的属性进行快速查询。例如 “character” 和 “location” 都有primaryKeys("name")属性，因此在不额外创建索引的情况下可以通过g.V().hasLabel('character') .has('name','hercules')查询vertex 。

3 Graph Traversal Examples

3.1 Traversal Query

1. Find the grandfather of hercules

g.V().hasLabel('character').has('name','hercules').out('father').out('father')

也可以通过repeat方式：

g.V().hasLabel('character').has('name','hercules').repeat(__.out('father')).times(2)

2. Find the name of hercules’s father

g.V().hasLabel('character').has('name','hercules').out('father').value('name')

3. Find the characters with age > 100

g.V().hasLabel('character').has('age',gt(100))

4. Find who are pluto’s cohabitants

g.V().hasLabel('character').has('name','pluto').out('lives').in('lives').values('name')

5. Find pluto can’t be his own cohabitant

pluto = g.V().hasLabel('character').has('name', 'pluto')
g.V(pluto).out('lives').in('lives').where(is(neq(pluto)).values('name')

// use 'as'
g.V().hasLabel('character').has('name', 'pluto').as('x').out('lives').in('lives').where(neq('x')).values('name')

6. Pluto’s Brothers

pluto = g.V().hasLabel('character').has('name', 'pluto').next()
// where do pluto's brothers live?
g.V(pluto).out('brother').out('lives').values('name')

// which brother lives in which place?
g.V(pluto).out('brother').as('god').out('lives').as('place').select('god','place')

// what is the name of the brother and the name of the place?
g.V(pluto).out('brother').as('god').out('lives').as('place').select('god','place').by('name')

推荐使用HugeGraph-Studio 通过可视化的方式来执行上述代码。另外也可以通过HugeGraph-Client、HugeApi、GremlinConsole和GremlinDriver等多种方式执行上述代码。

3.2 总结

HugeGraph 目前支持 Gremlin 的语法，用户可以通过 Gremlin / REST-API 实现各种查询需求。