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
当两个接口（里面的_typename同名）同时存在时就会出错。
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！
