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这个问题我已经经历过两三次了：*graphql 服务端定义接口时，千万不要把每个接口中的_typename写成一样的。
在go语言中，graphql 的实现里头， 错误的示例如下：

var responseDimensionReadingType = graphql.NewObject(graphql.ObjectConfig{
    Name: "ResponseCommon",
    Fields: graphql.Fields{
        "code":    &graphql.Field{Type: graphql.Int},
        "content": &graphql.Field{Type: graphql.NewList(dimensionReadingType)},
        "count":   &graphql.Field{Type: graphql.Int},
        "msg":     &graphql.Field{Type: messageType},
    },
    Description: "",
})
var responseDimensionWritingType = graphql.NewObject(graphql.ObjectConfig{
    Name: "ResponseCommon",
    Fields: graphql.Fields{
        "code":    &graphql.Field{Type: graphql.Int},
        "content": &graphql.Field{Type: graphql.NewList(dimensionWritingType)},
        "count":   &graphql.Field{Type: graphql.Int},
        "msg":     &graphql.Field{Type: messageType},
    },
    Description: "",
})

• 可以看到，这两个graphql类型定义中，都将 Name 写成了 ResponseCommon
• 这个 Name 对应的就是前面说的 _typename
  
  

  _typename

当两个接口（里面的_typename同名）同时存在时就会出错。

触发报错

报错如下：

{"data":null,"errors":[{"message":"Variable \"$from_id\" cannot be non-input type \"String!\".","locations":[{"line":1,"column":34}]},{"message":"Unknown type \"String\".","locations":[{"line":1,"column":34}]},{"message":"Variable \"$from_nickname\" cannot be non-input type \"String!\".","locations":[{"line":1,"column":59}]},{"message":"Unknown type \"String\".","locations":[{"line":1,"column":59}]},{"message":"Variable \"$content\" cannot be non-input type \"String!\".","locations":[{"line":1,"column":78}]},{"message":"Unknown type \"String\".","locations":[{"line":1,"column":78}]},{"message":"Variable \"$from_id\" of type \"\" used in position expecting type \"String!\".","locations":[{"line":1,"column":24},{"line":3,"column":14}]},{"message":"Variable \"$content\" of type \"\" used in position expecting type \"String!\".","locations":[{"line":1,"column":68},{"line":4,"column":14}]},{"message":"Variable \"$from_nickname\" of type \"\" used in position expecting type \"String!\".","locations":[{"line":1,"column":43},{"line":5,"column":20}]}]}

• 报错信息，我是没明白啥意思，顺着报错信息找问题，一点头绪都没。

调查这个问题时，感觉离谱之处在于：我随便保留两个接口中的其中一个，都不会有问题，两个接口同时出现才会报错。

记忆中，第一次出现这个问题，我debug，debug了一天没找着原因，后来还是整整回滚了一个版本的代码才解决；第二次遇到这个问题，也是花了好久才知道是_typename的事儿。这次必须记下来，警醒自己！