json schema 快速入门

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2016-12-24
原文链接:www.jianshu.com

Json Schema 快速入门

JSON 模式是一种基于 JSON 格式定义 JSON 数据结构的规范。它被写在 IETF 草案下并于 2011 年到期。JSON 模式:

  • 描述现有数据格式。
  • 干净的人类和机器可读的文档。
  • 完整的结构验证,有利于自动化测试。
  • 完整的结构验证,可用于验证客户端提交的数据。

Json schema 格式

Json schema 本身遵循Json规范,本身就是一个Json字符串,先来看一个例子

{
    "$schema": "http://json-schema.org/draft-04/schema#",
    "title": "Product",
    "description": "A product from Acme's catalog",
    "type": "object",
    "properties": {
        "id": {
            "description": "The unique identifier for a product",
            "type": "integer"
        },
        "name": {
            "description": "Name of the product",
            "type": "string"
        },
        "price": {
            "type": "number",
            "minimum": 0,
            "exclusiveMinimum": true
        }
    },
    "required": ["id", "name", "price"]
}

我们来看一下json schema 最外层包含以下几个字段

$schema 描述 示例
$schema $schema 关键字状态,表示这个模式与 v4 规范草案书写一致。
title 标题,用来描述结构
description 描述
type 类型 .
properties 定义属性
required 必需属性

上面只是一个简单的例子,从上面可以看出Json schema 本身是一个JSON字符串,由通过key-value的形式进行标示。
type 和 properties 用来定义json 属性的类型。required 是对Object字段的必段性进行约束。事实上,json Schema定义了json所支持的类型,每种类型都有0-N种约束方式。下一节我们来,细致介绍一下。


Json schema 类型

Object

{
    "$schema": "http://json-schema.org/draft-04/schema#",
    "title": "Product",
    "description": "A product from Acme's catalog",
    "type": "object",
    "properties": {
        "id": {
            "description": "The unique identifier for a product",
            "type": "integer"
        },
        "name": {
            "description": "Name of the product",
            "type": "string"
        },
        "price": {
            "type": "number",
            "minimum": 0,
            "exclusiveMinimum": true
        }
    },
    "required": ["id", "name", "price"]
}

object类型有三个关键字:type(限定类型),properties(定义object的各个字段),required(限定必需字段),如下:
| 关键字 | 描述 | 示例 |
|:------------- |:---------------| ----- |
| type |类型|. |
| properties |定义属性||
| required|必需属性||
| maxProperties |最大属性个数||
| minProperties |最小属性个数||
| additionalProperties |true or false or object|参考|
properties 定义每个属性的名字和类型,方式如上例。

array

{
    "$schema": "http://json-schema.org/draft-04/schema#",
    "title": "Product",
    "description": "A product from Acme's catalog",
    "type": "array",
    "items": {
        "type": "string"
     },
     "minItems": 1,
     "uniqueItems": true
    }

array有三个单独的属性:items,minItems,uniqueItems:

关键字 描述 示例
items array 每个元素的类型 .
minItems 约束属性,数组最小的元素个数
maxItems 约束属性,数组最大的元素个数
uniqueItems 约束属性,每个元素都不相同
additionalProperties 约束items的类型,不建议使用 示例
Dependencies 属性依赖 用法
patternProperties 用法

string

{
   "$schema": "http://json-schema.org/draft-04/schema#",
    "title": "Product",
    "description": "A product from Acme's catalog",
    "type": "object",
    "properties": {
        "ip": {
            "mail": "string",
            "pattern":"w+([-+.]w+)*@w+([-.]w+)*.w+([-.]w+)*"
        },
        "host": {
            "type": "phoneNumber",
            "pattern":"((d{3,4})|d{3,4}-)?d{7,8}(-d{3})*"
        },
    },
    "required": ["ip", "host"]
}
关键字 描述 示例
maxLength 定义字符串的最大长度,>=0 .
minLength 定义字符串的最小长度,>=0
pattern 用正则表达式约束字符串

integer

{
    "$schema": "http://json-schema.org/draft-04/schema#",
    "title": "Product",
    "description": "A product from Acme's catalog",
    "type": "object",
    "properties": {
        "name": {
            "description": "Name of the product",
            "type": "string"
        },
        "price": {
            "type": "integer",
            "minimum": 0,
            "exclusiveMinimum": true
        }
    },
    "required": ["id", "name", "price"]
}

number

{
    "$schema": "http://json-schema.org/draft-04/schema#",
    "title": "Product",
    "description": "A product from Acme's catalog",
    "type": "object",
    "properties": {
        "name": {
            "description": "Name of the product",
            "type": "string"
        },
        "price": {
            "type": "number",
            "minimum": 0,
            "exclusiveMinimum": true
        }
    },
    "required": ["id", "name", "price"]
}

| 关键字      | 描述  |    示例   |
|:------------- |:---------------| ----- |
| minimum |最小值|. |
| exclusiveMinimum |如果存在 "exclusiveMinimum" 并且具有布尔值 true,如果它严格意义上大于 "minimum" 的值则实例有效。||
| maximum |约束属性,最大值||
| exclusiveMaximum |如果存在 "exclusiveMinimum" 并且具有布尔值 true,如果它严格意义上小于 "maximum" 的值则实例有效。||
| multipleOf |是某数的倍数,必须大于0的整数||

number 关键字可以描述任意长度,任意小数点的数字。number类型的约束有以下几个:

关键字 描述 示例
minimum 最小值 .
exclusiveMinimum 如果存在 "exclusiveMinimum" 并且具有布尔值 true,如果它严格意义上大于 "minimum" 的值则实例有效。
maximum 约束属性,最大值
exclusiveMaximum 如果存在 "exclusiveMinimum" 并且具有布尔值 true,如果它严格意义上小于 "maximum" 的值则实例有效。

boolean

{
"type": "object",
"properties": {
"number": { "type": "boolean" },
"street_name": { "type": "string" },
"street_type": { "type": "string",
"enum": ["Street", "Avenue", "Boulevard"]
}
}
}
true or false

enum

{
  "type": "object",
  "properties": {
    "number":      { "type": "number" },
    "street_name": { "type": "string" },
    "street_type": { "type": "string",
                     "enum": ["Street", "Avenue", "Boulevard"]
                   }
  }
}

也可以这么做

{
  "type": "object",
  "properties": {
    "number":      { "type": "number" },
    "street_name": { "type": "string" },
    "street_type": ["Street", "Avenue", "Boulevard"]                   
  }
}

null

进阶

了解了上面的各个类型的定义及约定条件,就可以满足大部分情况了。但为了写出更好的json schema,我们再学习几个关键字

$ref

$ref 用来引用其它schema,
示例如下:

{
    "$schema": "http://json-schema.org/draft-04/schema#",
    "title": "Product set",
    "type": "array",
    "items": {
        "title": "Product",
        "type": "object",
        "properties": {
            "id": {
                "description": "The unique identifier for a product",
                "type": "number"
            },
            "name": {
                "type": "string"
            },
            "price": {
                "type": "number",
                "minimum": 0,
                "exclusiveMinimum": true
            },
            "tags": {
                "type": "array",
                "items": {
                    "type": "string"
                },
                "minItems": 1,
                "uniqueItems": true
            },
            "dimensions": {
                "type": "object",
                "properties": {
                    "length": {"type": "number"},
                    "width": {"type": "number"},
                    "height": {"type": "number"}
                },
                "required": ["length", "width", "height"]
            },
            "warehouseLocation": {
                "description": "Coordinates of the warehouse with the product",
                "$ref": "http://json-schema.org/geo"
            }
        },
        "required": ["id", "name", "price"]
    }
}

definitions

当一个schema写的很大的时候,可能需要创建内部结构体,再使用$ref进行引用,示列如下:

{
    "type": "array",
    "items": { "$ref": "#/definitions/positiveInteger" },
    "definitions": {
        "positiveInteger": {
            "type": "integer",
            "minimum": 0,
            "exclusiveMinimum": true
        }
    }
}

allOf

意思是展示全部属性,建议用requires替代

不建议使用,示例如下

{
  "definitions": {
    "address": {
      "type": "object",
      "properties": {
        "street_address": { "type": "string" },
        "city":           { "type": "string" },
        "state":          { "type": "string" }
      },
      "required": ["street_address", "city", "state"]
    }
  },

  "allOf": [
    { "$ref": "#/definitions/address" },
    { "properties": {
        "type": { "enum": [ "residential", "business" ] }
      }
    }
  ]
}

anyOf

意思是展示任意属性,建议用requires替代和minProperties替代,示例如下:

{
  "anyOf": [
    { "type": "string" },
    { "type": "number" }
  ]
}

oneOf

其中之一

{
  "oneOf": [
    { "type": "number", "multipleOf": 5 },
    { "type": "number", "multipleOf": 3 }
  ]
}

not

非 * 类型
示例

{ "not": { "type": "string" } }

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