如何处理从mongo返回的任意散列（使用mgo）？ [英] How do I deal with an arbitrary hash returned from mongo in go (using mgo)?

问题描述

假设每个返回的记录具有相同的模式，我可以找到的所有引用构造一个结构来保存返回值。如果它们确实是文档，并且除了可能的几个可查询的一致元数据属性之外没有一致的模式，我该如何处理该返回值？

例如：this https://groups.google.com/forum/#!msg / mgo-users / KirqfCSlKFc / t2l3l4yxFRwJ 假定您有一组时间戳。如果是一个数组，其中一些值是时间戳，一些是字符串呢？

在ruby中，我只是将整个返回的记录视为任意散列和交易与它按键。

解决方案

您可以使用通用映射，例如：

  var result map [string] interface {} 
 err：= collection.Find（query）.One（& result）
  

您会发现使用 bson.M 的人，其中也是具有相同基础类型的地图。不过，没有什么特别的 bson.M 。这只是地图的一个简短而方便的名字。您可以创建自己的便捷名称，或使用上面示例中的普通映射。

另一种访问不带定义模式的文档的方法是使用 bson.D 来代替上面的地图类型。 bson.D 在文档中元素的顺序是相关的时候最为有用，或者如果您想稍微减少操作开销（地图的处理效果会更加昂贵对其性质）。 bson.D 类型是带有键/值对的一段结构值。不同于 bson.M ， bson.D 是特殊的，并且由mgo / bson包内部处理。

All of the references I can find construct a struct to hold the return values, assuming that each returned record has the same schema. If they're really documents and don't have a consistent schema other than maybe a few queryable consistent metadata attributes, how can I handle that return value?

e.g.: this https://groups.google.com/forum/#!msg/mgo-users/KirqfCSlKFc/t2l3l4yxFRwJ assumes that you have an array of timestamps. What if it's an array where some of the values are timestamps and some are strings?

In ruby, I'd just treat the whole returned record as an arbitrary hash and deal with it key by key. What can I do with it in go?

解决方案

You can use a generic map, for example:

var result map[string]interface{}
err := collection.Find(query).One(&result)

You'll find people using bson.M, which is also a map with that same underlying type. There's nothing special about bson.M, though. It's just a short and convenient name for a map. You can create your own convenient name, or use a plain map as in the example above.

Another way to have access to documents without a defined schema is using bson.D in place of the map type above. bson.D is most useful when the order of elements in the document is relevant, or if you want to reduce the operation overhead slightly (maps are a bit more expensive to handle due to their nature). The bson.D type is a slice of struct values with Key/Value pairs. Unlike bson.M, bson.D is special and is handled internally by the mgo/bson package.

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