为什么该JSON Schema无法赋值给对应的TypeScript接口类型？

报错原因 #

存在两处类型不匹配问题：

• 字段类型定义错误：你在schema的changes数组项规则中，将old、new字段的类型设置为string，但ExpectedBody接口中这两个字段是包含name属性的对象，二者类型完全不兼容。
• 元组与普通数组定义不匹配：接口中changes的类型是[{old:..., new:...}]，属于TypeScript固定长度为1的元组类型，要求数组必须有且仅有1个符合规则的元素；但你在schema中将该字段定义为minItems: 0的普通数组，和元组的类型要求不符。

修复方案 #

可根据你的实际业务需求二选一：

方案1：确实需要changes为固定长度1的元组 #

调整schema的changes字段配置，同时修正old、new的类型定义：

import Ajv, { JSONSchemaType } from 'ajv'

interface ExpectedBody {
    repository: {
      name: string,
    }
    push: {
      changes: [{
        old: {
          name: string,
        },
        new: {
          name: string,
        }
      }]
    }
  }
  
  const expectedBodySchema: JSONSchemaType<ExpectedBody> = {
    type: 'object',
    properties: {
      repository: {
        type: 'object',
        properties: {
          name: {
            type: 'string',
          },
        },
        required: ['name'],
      },
      push: {
        type: 'object',
        properties: {
          changes: {
            type: 'array',
            // 匹配元组固定长度1的要求
            minItems: 1,
            maxItems: 1,
            // 元组的items需要用数组格式，对应每个位置的元素规则
            items: [
              {
                type: 'object',
                properties: {
                  old: {
                    type: 'object',
                    properties: {
                      name: { type: 'string' }
                    },
                    required: ['name']
                  },
                  new: {
                    type: 'object',
                    properties: {
                      name: { type: 'string' }
                    },
                    required: ['name']
                  },
                },
                required: ['old', 'new']
              }
            ],
          },
        },
        required: ['changes']
      }
    },
    required: ['repository', 'push'],
  }

方案2：需要changes为任意长度的普通数组 #

先修改接口定义，将元组改为普通数组，再对应调整schema：

import Ajv, { JSONSchemaType } from 'ajv'

interface ExpectedBody {
    repository: {
      name: string,
    }
    push: {
      // 元组改为普通数组定义
      changes: Array<{
        old: {
          name: string,
        },
        new: {
          name: string,
        }
      }>
    }
  }
  
  const expectedBodySchema: JSONSchemaType<ExpectedBody> = {
    type: 'object',
    properties: {
      repository: {
        type: 'object',
        properties: {
          name: {
            type: 'string',
          },
        },
        required: ['name'],
      },
      push: {
        type: 'object',
        properties: {
          changes: {
            type: 'array',
            minItems: 0,
            items: {
              type: 'object',
              properties: {
                old: {
                  type: 'object',
                  properties: {
                    name: { type: 'string' }
                  },
                  required: ['name']
                },
                new: {
                  type: 'object',
                  properties: {
                    name: { type: 'string' }
                  },
                  required: ['name']
                },
              },
              required: ['old', 'new']
            },
          },
        },
        required: ['changes']
      }
    },
    required: ['repository', 'push'],
  }

内容的提问来源于stack exchange，提问作者user1283776