详解Python Graphql

大朗喝药啦 發表於 2019-10-16 12:14:00

<h1>前言</h1>
很高兴现在接手的项目让我接触到了Python Graphql，百度上对其介绍相对较少也不够全面，几乎没有完整的中文文档，所以这边也借此机会学习一下Graphql。
什么是Graphql呢？
Graphql是一个API查询语言，其数据由服务器上的一个Scheme提供，其查询返回的数据依赖请求的时候用户需要的精确数据。列如用户只需要一个name字段，服务器也只返回name的值。
参考
英文学习文档：https://graphene-python.org/
更多example关注：https://github.com/graphql-python/graphene/tree/master/examples
<h1>Hello Word 入门</h1>
先看下面一个例子，查询语句为{ hello(name:"gaojiayi") } 定义了要查询的入口，以及传入的参数。
<div class="cnblogs_code">
<pre>from graphene import ObjectType, String, Schema

class Query(ObjectType):
"""定义一个字符串属性域hello 且有一个字符串参数为name，设置name的默认"""
hello = String(name = String(default_value="gaojy",required=True))

# resolve_hello定义了上面hello的实现，并返回查询结果
# 一般resolve需要加上固定前缀resolve_
 @staticmethod
def resolve_hello(root,info,name):
 return f"hello word -- {name}"

schema = Schema(query=Query)

if __name__ == '__main__':
query_string = '''{ hello(name:"gaojiayi") }'''
result = schema.execute(query_string)
print(result.data['hello'])</pre>
</div>
<h1> Graphql中的Types</h1>
<h2>Scheme</h2>
下面定义了一个Scheme，其中MyRootQuery，MyRootMutation，MyRootSubscription都是继承了graphene .objectType,但是不同之处在于query定义了查询数据的入口，而mutation用来数据改变或者数据恢复，而subscription是用来实时呈现数据的变化给client。type是用来指定返回数据的精确类型，列如返回的数据是一个interface，但是有多个类型继承了该interface，这时候需要指定一个具体的实现来返回给client。
<div class="cnblogs_code">
<pre>my_schema = Schema(
query=MyRootQuery,
mutation=MyRootMutation,
subscription=MyRootSubscription, 　　 type=[SomeExtraObjectType,] )</pre>
</div>
另外查询字符串默认为驼峰命名，列如
<div class="cnblogs_code">
<pre>from graphene import ObjectType, String, Schema

class Query(ObjectType):
other_name = String(name='_other_Name')

@staticmethod
def resolve_other_name(root, info):
 return "test CamelCase"

schema = Schema(query=Query)

if __name__ == '__main__':
# 查询数默认使用otherName，此处用了别名。
result = schema.execute('''{_other_Name}''')
print(result.data['_other_Name'])</pre>
</div>
如果关闭默认驼峰命名方式，则可以在定义scheme的时候加上auto_camelcase=False
<pre>my_schema = Schema(
 auto_camelcase=False
) </pre>
<h2>scalars</h2>
scalars type可以理解为用来定义Field，它可以传入以下几种可选参数，例如
other_name = String(name='_other_Name',required=True,description="",deprecation_reason="",defalut_value=Any)
 
常见的基本saclars type有如下几个：
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<div id="cnblogs_code_open_3686ec43-9740-4fc5-ba13-2b0cf17dbb20" class="cnblogs_code_hide">
<pre>graphene.String
graphene.Int
graphene.Float
graphene.Boolean
graphene.ID
graphene.types.datetime.Date
graphene.types.datetime.DateTime
graphene.types.datetime.Time
graphene.types.json.JSONString</pre>
</div>
View Code</div>
 
saclars type的挂载在objectType,interface,Mutation中的field域中。
<div class="cnblogs_code"><img id="code_img_closed_b6aa42af-2bdf-4539-94b0-6c532301ab27" class="code_img_closed lazyload" alt="" data-src="http://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif"><img id="code_img_opened_b6aa42af-2bdf-4539-94b0-6c532301ab27" class="code_img_opened lazyload" style="display: none" alt="" data-src="http://images.cnblogs.com/OutliningIndicators/ExpandedBlockStart.gif">
<div id="cnblogs_code_open_b6aa42af-2bdf-4539-94b0-6c532301ab27" class="cnblogs_code_hide">
<pre>class Person(graphene.ObjectType):
name = graphene.String()

# Is equivalent to:
class Person(graphene.ObjectType):
name = graphene.Field(graphene.String)</pre>
</div>
View Code</div>
 
<h2>Lists and Non-Null</h2>
Non-Null
<div class="cnblogs_code">
<pre>import graphene

class Character(graphene.ObjectType):
name = graphene.String(required=True)
#等价于即返回的数据如果name=null，则会报错
class Character(graphene.ObjectType):
name = graphene.String(required=True)</pre>
</div>
Lists
<div class="cnblogs_code">
<pre>import graphene

class Character(graphene.ObjectType):
# appears_in表示为一个非null元素的列表
appears_in = graphene.List(graphene.NonNull(graphene.String))</pre>
</div>
<h2> </h2>
<h2>ObjectType</h2>
objectType是在scheme中用来定义Fields之间联系以及数据流转的python类，每一个obejctType属性表示一个Field，每个Field定义一个resolve方法用来获取数据，如果没有定义，则使用一个默认的resolver。
 接下来看一个例子。
<div class="cnblogs_code">
<pre>from graphene import ObjectType, String, Schema

class Query(ObjectType):
@staticmethod
def resolve_hello(parent,info,name):
 return f"hello word -- {name}"</pre>
</div>
上面的resolve_hello有三个参数，分别是parent，info，name
1 parent通常用来获取objectType内的其他field的值，而在根query中默认为None，看下面的事例，当OjectType的Field为saclar type，则parent不会再向下传递。
<div class="cnblogs_code"><img id="code_img_closed_834df17a-bd82-4e6d-b999-6785e7060f70" class="code_img_closed lazyload" alt="" data-src="http://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif"><img id="code_img_opened_834df17a-bd82-4e6d-b999-6785e7060f70" class="code_img_opened lazyload" style="display: none" alt="" data-src="http://images.cnblogs.com/OutliningIndicators/ExpandedBlockStart.gif">
<div id="cnblogs_code_open_834df17a-bd82-4e6d-b999-6785e7060f70" class="cnblogs_code_hide">
<pre>class Person(ObjectType):
full_name = String()

def resolve_full_name(parent, info):
 return f"{parent.first_name} {parent.last_name}"

class Query(ObjectType):
me = Field(Person)

def resolve_me(parent, info):
 # returns an object that represents a Person
 # 这里的parent为None
 return get_human(name="Luke Skywalker")</pre>
</div>
View Code</div>
当然，根查询的parent也可以初始化值，就是在execute的时候添加root变量
<div class="cnblogs_code"><img id="code_img_closed_8e285880-13ae-44a4-a81a-4a62b3f96c01" class="code_img_closed lazyload" alt="" data-src="http://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif"><img id="code_img_opened_8e285880-13ae-44a4-a81a-4a62b3f96c01" class="code_img_opened lazyload" style="display: none" alt="" data-src="http://images.cnblogs.com/OutliningIndicators/ExpandedBlockStart.gif">
<div id="cnblogs_code_open_8e285880-13ae-44a4-a81a-4a62b3f96c01" class="cnblogs_code_hide">
<pre> @staticmethod
def resolve_hello(parent, info, name):
 # 打印结果 man ，parent默认为root的值
 print(parent['sex'])
 return f"hello word -- {name}"

schema = Schema(query=Query, mutation=MyMutations)

if __name__ == '__main__':
query_string = '''{ hello(name:"gaojiayi") }'''
# 指定root的值
result = schema.execute(query_string, root={'sex': 'man'})
print(result.data['hello'])</pre>
</div>
View Code</div>
当查询语句存在多个的时候，可指定执行那一条语句
<div class="cnblogs_code"><img id="code_img_closed_32716bb5-ad29-46af-8cdd-f8db896ab0e1" class="code_img_closed lazyload" alt="" data-src="http://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif"><img id="code_img_opened_32716bb5-ad29-46af-8cdd-f8db896ab0e1" class="code_img_opened lazyload" style="display: none" alt="" data-src="http://images.cnblogs.com/OutliningIndicators/ExpandedBlockStart.gif">
<div id="cnblogs_code_open_32716bb5-ad29-46af-8cdd-f8db896ab0e1" class="cnblogs_code_hide">
<pre>schema = Schema(Query)
query_string = '''
query getUserWithFirstName {
 user {
 id
 firstName
 lastName
 }
}
query getUserWithFullName {
 user {
 id
 fullName
 }
}
'''
result = schema.execute(
query_string,
# 指定执行第二条语句
operation_name='getUserWithFullName'
)</pre>
</div>
View Code</div>
2 info表示请求的上下文，可以在查询语中添加context，列如
<div class="cnblogs_code"><img id="code_img_closed_c81ddd40-5c04-499f-8b2a-e0edaa3207bc" class="code_img_closed lazyload" alt="" data-src="http://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif"><img id="code_img_opened_c81ddd40-5c04-499f-8b2a-e0edaa3207bc" class="code_img_opened lazyload" style="display: none" alt="" data-src="http://images.cnblogs.com/OutliningIndicators/ExpandedBlockStart.gif">
<div id="cnblogs_code_open_c81ddd40-5c04-499f-8b2a-e0edaa3207bc" class="cnblogs_code_hide">
<pre>class Query(ObjectType):
hello = String(name=String(default_value="gaojy", required=True))
@staticmethod
def resolve_hello(root, info, name):
 # 通过info可获取上下文内容
 print(info.context.get('company'))
 return f"hello word -- {name}"

schema = Schema(query=Query, mutation=MyMutations)

if __name__ == '__main__':
query_string = '''{ hello(name:"gaojiayi") }'''
# 1 execute中添加context
result = schema.execute(query_string, context={'company': 'baidu'})
print(result.data['hello'])</pre>
</div>
View Code</div>
3 name表示请求时带的参数，可以参考hello word事例，如有多个参数可形参**kwargs
<div class="cnblogs_code"><img id="code_img_closed_e08ae7ea-778e-4afb-a15d-edbaae634434" class="code_img_closed lazyload" alt="" data-src="http://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif"><img id="code_img_opened_e08ae7ea-778e-4afb-a15d-edbaae634434" class="code_img_opened lazyload" style="display: none" alt="" data-src="http://images.cnblogs.com/OutliningIndicators/ExpandedBlockStart.gif">
<div id="cnblogs_code_open_e08ae7ea-778e-4afb-a15d-edbaae634434" class="cnblogs_code_hide">
<pre>from graphene import ObjectType, String

class Query(ObjectType):
hello = String(required=True, name=String())

def resolve_hello(parent, info, **kwargs):
 # name 为None 则name = World
 name = kwargs.get('name', 'World')
 return f'Hello, {name}!'</pre>
</div>
View Code</div>
4 默认resolver：列如一个objectType的field都没有指定队友的resolve，那么对象默认会序列化一个字典。
<div class="cnblogs_code"><img id="code_img_closed_6d1e7906-d2c5-4afe-83e6-b04ddec309e2" class="code_img_closed lazyload" alt="" data-src="http://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif"><img id="code_img_opened_6d1e7906-d2c5-4afe-83e6-b04ddec309e2" class="code_img_opened lazyload" style="display: none" alt="" data-src="http://images.cnblogs.com/OutliningIndicators/ExpandedBlockStart.gif">
<div id="cnblogs_code_open_6d1e7906-d2c5-4afe-83e6-b04ddec309e2" class="cnblogs_code_hide">
<pre>PersonValueObject = namedtuple('Person', 'first_name', 'last_name')

class Person(ObjectType):
first_name = String()
last_name = String()

class Query(ObjectType):
me = Field(Person)
my_best_friend = Field(Person)

def resolve_me(parent, info):
 # always pass an object for `me` field
 # {"firstName": "Luke", "lastName": "Skywalker"}
 return PersonValueObject(first_name='Luke', last_name='Skywalker')</pre>
</div>
View Code</div>
 5 meta 类：用于objectType的配置
<h2>Enum</h2>
<div class="cnblogs_code"><img id="code_img_closed_a528945f-7258-442d-bed1-5f1054adaba2" class="code_img_closed lazyload" alt="" data-src="http://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif"><img id="code_img_opened_a528945f-7258-442d-bed1-5f1054adaba2" class="code_img_opened lazyload" style="display: none" alt="" data-src="http://images.cnblogs.com/OutliningIndicators/ExpandedBlockStart.gif">
<div id="cnblogs_code_open_a528945f-7258-442d-bed1-5f1054adaba2" class="cnblogs_code_hide">
<pre>class Episode(graphene.Enum):
NEWHOPE = 4
EMPIRE = 5
JEDI = 6

@property
def description(self):
 if self == Episode.NEWHOPE:
 return 'New Hope Episode'
 return 'Other episode'

class Query(ObjectType):
 desc1 = String(
 v=Argument(Episode, default_value=Episode.NEWHOPE.value),
 description='default value in schema is `4`, which is not valid. Also, awkward to write.')

@staticmethod
def resolve_desc1(parent, info,v):
 return f'argument: {v!r}'

# 使用下面的方式可以将python类型的enum转化成saclars类型
graphene.Enum.from_enum(
AlreadyExistingPyEnum,
description=lambda v: return 'foo' if v == AlreadyExistingPyEnum.Foo else 'bar')</pre>
</div>
View Code</div>
<h2>Interfaces</h2>
顾名思义，接口，其他的obectType可以继承接口，示例如下
<div class="cnblogs_code"><img id="code_img_closed_838a258d-9d1d-477a-991f-5574a3f2e8fd" class="code_img_closed lazyload" alt="" data-src="http://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif"><img id="code_img_opened_838a258d-9d1d-477a-991f-5574a3f2e8fd" class="code_img_opened lazyload" style="display: none" alt="" data-src="http://images.cnblogs.com/OutliningIndicators/ExpandedBlockStart.gif">
<div id="cnblogs_code_open_838a258d-9d1d-477a-991f-5574a3f2e8fd" class="cnblogs_code_hide">
<pre>import graphene

class Character(graphene.Interface):
id = graphene.ID(required=True)
name = graphene.String(required=True)
friends = graphene.List(lambda: Character)

#继承Character
class Human(graphene.ObjectType):
class Meta:
 interfaces = (Character, )

starships = graphene.List(Starship)
home_planet = graphene.String()

#继承Character
class Droid(graphene.ObjectType):
class Meta:
 interfaces = (Character, )

primary_function = graphene.String()

class Query(graphene.ObjectType):
# 返回的类型是Character
hero = graphene.Field(
 Character,
 required=True,
 episode=graphene.Int(required=True)
)

def resolve_hero(root, info, episode):
 # Luke is the hero of Episode V
 if episode == 5:
 return get_human(name='Luke Skywalker')
 return get_droid(name='R2-D2')

#对于返回数据具体类型，可以在type属性中列举
schema = graphene.Schema(query=Query, types=)</pre>
</div>
View Code</div>
另外scheme中如果没有指定type，会报错
"Abstract type Character must resolve to an Object type at runtime for field Query.hero ..."
可以在interface中重写resolve_type方法
<div class="cnblogs_code">
<pre>class Character(graphene.Interface):
id = graphene.ID(required=True)
name = graphene.String(required=True)
#返回数据的时候，可以转换成具体的数据类型
 @classmethod
def resolve_type(cls, instance, info):
 if instance.type == 'DROID':
 return Droid
 return Human</pre>
</div>
<h2>Union</h2>
该scalars type用来组合多个ObjectType，列如
<div class="cnblogs_code"><img id="code_img_closed_7e70906f-e253-4fa0-bc03-c0cfc970f023" class="code_img_closed lazyload" alt="" data-src="http://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif"><img id="code_img_opened_7e70906f-e253-4fa0-bc03-c0cfc970f023" class="code_img_opened lazyload" style="display: none" alt="" data-src="http://images.cnblogs.com/OutliningIndicators/ExpandedBlockStart.gif">
<div id="cnblogs_code_open_7e70906f-e253-4fa0-bc03-c0cfc970f023" class="cnblogs_code_hide">
<pre>import graphene

class Human(graphene.ObjectType):
name = graphene.String()
born_in = graphene.String()

class Droid(graphene.ObjectType):
name = graphene.String()
primary_function = graphene.String()

class Starship(graphene.ObjectType):
name = graphene.String()
length = graphene.Int()
# SearchResult组合了Human Droid Starship所有的Fields
class SearchResult(graphene.Union):
class Meta:
 types = (Human, Droid, Starship)</pre>
</div>
View Code</div>
<h2>Mutations</h2>
如果说query是一个http get请求，那么Mutations可以看做是一个http post put请求。
def Mutate作为一个特殊的resover，当被调用的时候意在改变Mutation内的数据。
看下面一个操作示例
<div class="cnblogs_code">
<pre>#具体的操作类
class CreatePerson(graphene.Mutation):
# 请求提交的参数，同样需要传递到mutate中
class Arguments:
 name = graphene.String()

ok = graphene.Boolean()
person = graphene.Field(Person)

def mutate(root, info, name):
 person = Person(name=name)
 ok = True
 #可执行具体的业务逻辑包括写表发消息等等
 return CreatePerson(person=person, ok=ok)

# Mutation
class MyMutations(graphene.ObjectType):
create_person = CreatePerson.Field()
#指定mutationMyMutations
schema = Schema(query=Query,mutation=MyMutations)</pre>
</div>
执行结果如下：
<img alt="" width="633" height="174" data-src="https://img2018.cnblogs.com/blog/1135670/201910/1135670-20191016120429772-494033859.png">
 
Mutation下可申明InputFields 和InputObjectTypes类型的出入参，其中InputFields可以定义复合型入参，Output可指定复合型出参。
例1：InputFields 
<div class="cnblogs_code">
<pre>class DataInput(graphene.InputObjectType):
user_name = String()
basic_age = Int()

class Person(graphene.ObjectType):
name = graphene.String()
age = graphene.Int()

# 具体的操作类
class CreatePerson(graphene.Mutation):
# 请求提交的参数，同样需要传递到mutate中
class Arguments:
 data = DataInput(required=True)

ok = graphene.Boolean()
person = graphene.Field(Person)

def mutate(root, info, data):
 person = Person(name=data.user_name, age=data.basic_age * 10)
 ok = True
 return CreatePerson(person=person, ok=ok)</pre>
</div>
执行结果：
<img src="https://img2018.cnblogs.com/blog/1135670/201910/1135670-20191016155500099-589337239.png">
 
 例2：InputObjectTypes
<div class="cnblogs_code">
<pre>class DataInput(graphene.InputObjectType):
user_name = String()
basic_age = Int()

class Person(graphene.ObjectType):
name = graphene.String()
age = graphene.Int()

# 具体的操作类
class CreatePerson(graphene.Mutation):
# 请求提交的参数，同样需要传递到mutate中
class Arguments:
 data = DataInput(required=True)
# 定义一个Output 且指定class ，在mutate方法中返回实例
Output = Person
def mutate(root, info, data):
 person = Person(name=data.user_name, age=data.basic_age * 10)
 return person</pre>
</div>
运行结果：
<img src="https://img2018.cnblogs.com/blog/1135670/201910/1135670-20191016155842949-353858570.png">
<h1> relay</h1>
relay类似于react js中的redux，VUE中的vuex，可以缓存server端数据，加快查询并提供更新机制。example可参考前言中的example。
 
<h1>小结</h1>
 　技术本身就是为业务服务，读者会问Graphql究竟可以使用在哪些业务场景呢？
　官方有这么一句话ask exactly what you want.如果一个前端的接口只需要返回部分数据，而另一个前端接口也只需要返回部分数据，这两份数据有可能有交集，也可能没有。传统的做法可能需要开发两个接口或者一个接口内不断的if else来根据前端的具体场景去过滤某些数据。使用Graphql能够根据client指定需要哪些参数，后端scheme返回哪些参数，而后端只需要一个API可以查询到数据全集，Graphql可以自动完成数据解析，封装，过滤操作。
 
<pre></pre> 
来源：https://www.cnblogs.com/gaojy/p/11678191.html

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详解Python Graphql