mgo:如何更新文档中的特定数组

Question

我在我的数据库中有这个文件

[
  {
    "_id": "53dc97bf91f1f933e15d6fb1",
    "attributes": {
      "chilled": false,
      "flammable": false,
      "food": false,
      "fragile": false,
      "frozen": false,
      "hot": false,
      "outsized": false
    },
    "createdAt": "02/08/14 09:48:16",
    "customer": "53d68bc091f1f933e15d6f90",
    "location": [
      {
        "count": 0,
        "warehouse": "53db430c91f1f933e15d6fa6"
      },
      {
        "count": 34,
        "warehouse": "53db430c91g1f933e45d6fa4"
      },
    ],
    "name": "test",
    "type": "stored",
    "updatedAt": ""
  }
]

如果我知道仓库ID,我该如何更新位置数组？这就是我现在拥有的

coll := p.GetDb().C("product")
    changes := bson.M {
        "location": bson.M {
            "$elemMatch": bson.M {
                "warehouse": bson.ObjectIdHex(warehouseId),
            },
        },
        "$set": bson.M {
            "location.$.count": 4,
        }, 
    }

    err := coll.UpdateId(bson.ObjectIdHex(productId), changes)
    if err != nil {
        http.Error(res, err.Error(), 500)
        return
    }

但是得到这个错误:'location.$ elemMatch'中的美元($)前缀字段'$ elemMatch'对存储无效.

谢谢.

Answer 1

你用错误的方式写了这个.仓库"id"值的匹配属于您的对帐单的"查询"部分,而不是"更新"部分.因此,您不需要UpdateId变体,但Update因为它允许更广泛的查询选择:

query := bson.M{
    "_id": bson.ObjectIdHex(productId),
    "location.warehouse": bson.ObjectIdHex(warehouseId)
}

update := bson.M{
    "$set": bson.M{
        "location.$.count": 4
    }
}

err := coll.Update(query,update)

另请注意,"点符号"形式在这里很好,因为数组元素的选择器只是一个奇异的字段.您通常只需要$elemMatch在阵列中有多个字段来建立匹配时.