如何避免jsonschema解析$ref引用时向对应URI发起GET请求

要遵循JSON Schema规范使用$ref同时避免远程请求，你需要提前将本地定义的schema注册到jsonschema的解析器缓存中，让解析器遇到对应的$id时直接读取本地资源，而非发起远程请求。

完整实现代码 #

from jsonschema import validate, RefResolver

# 保留原有schema定义
point_schema = {
    "$id": "https://example.com/schemas/point",
    "type": "object",
    "properties": {"x": {"type": "number"}, "y": {"type": "number"}},
    "required": ["x", "y"],
}

polygon_schema = {
    "$id": "https://example.com/schemas/polygon",
    "type": "array",
    "items": {"$ref": "https://example.com/schemas/point"},
}

a_polygon = [{'x': 1, 'y': 2}, {'x': 3, 'y': 4}, {'x': 1, 'y': 2}]

# 构建本地schema映射：key为schema的$id，value为对应schema对象
local_schema_store = {
    point_schema["$id"]: point_schema,
    polygon_schema["$id"]: polygon_schema
}

# 创建自定义解析器，传入本地schema存储
resolver = RefResolver(
    base_uri=polygon_schema["$id"],
    referrer=polygon_schema,
    store=local_schema_store
)

# 校验时传入自定义解析器
validate(
    instance=a_polygon,
    schema=polygon_schema,
    resolver=resolver
)

方案说明 #

• 上述实现完全遵循JSON Schema的$ref规范，没有直接拼接字典
• 解析器遇到$ref对应的URI时，会优先查找local_schema_store中的本地schema，不会发起任何远程GET请求
• 如果有更多本地schema，只需要添加到local_schema_store字典中即可

替代简化方案 #

如果不需要拆分schema为独立的字典，也可以将公共schema放到当前schema的$defs字段中，使用本地相对引用，无需自定义解析器：

polygon_schema = {
    "$id": "https://example.com/schemas/polygon",
    "type": "array",
    "items": {"$ref": "#/$defs/point"},
    "$defs": {
        "point": {
            "type": "object",
            "properties": {"x": {"type": "number"}, "y": {"type": "number"}},
            "required": ["x", "y"],
        }
    }
}

a_polygon = [{'x': 1, 'y': 2}, {'x': 3, 'y': 4}, {'x': 1, 'y': 2}]
validate(instance=a_polygon, schema=polygon_schema)

这种方式的$ref指向当前schema内部的定义，天然不会触发远程请求，同样符合JSON Schema规范。

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