MongoDB找到内部数组

Question

我是 MongoDB 的新手，我想过滤一个内部数组。当前文档如下所示：

{
    "data1": "value1",
    "data2": "value2",
    ...
    "array1": [
        {
            "field1": field1value"
            "field2": field2value"
        },
        {
            "field1": expectedvalue"
            "field2": field2value"
        },
    ]
}

我希望得到如下结果：

{
    "data1": "value1",
    "data2": "value2",
    ...
    "array1": [
        {
            "field1": expectedvalue"
            "field2": field2value"
        },
    ]
}

我尝试按照In MongoDB, how do I search in an array of sub-documents? 和其他类似问题中的建议进行查找和汇总。

问题是我丢失了数组之外的所有信息（data1，data2，...）：

{
    "_id" : { "$oid" : "8001212651b8a68278edbc92"},
    "array1": [
        {
            "field1": expectedvalue"
            "field2": field2value"
        },
    ]
}

Answer 1

要仅返回 array1 数组中与给定条件匹配的子文档，您必须使用 project 和 filter（在 >= 3.2 版本中可用）。这是一个例子：

db.collection.aggregate([
    // this is optional, it is only included here to show you that you _can_ match 
    // the documents before you match the array of sub documents
    {$match: {data1: 'value1'}},
    {$project: {
            data1: 1,
            data2: 1,
            array1: {$filter: {
                input: '$array1',
                as: 'a',
                cond: {$eq: ['$$a.field1', 'expectedvalue']}
            }}
        }}
])

这将返回以下内容：

{
    "_id" : ...,
    "data1" : "value1",
    "data2" : "value2",
    "array1" : [ 
        {
            "field1" : "expectedvalue",
            "field2" : "field2value"
        }
    ]
}

您链接到的答案与 Mongo Java 驱动程序有关，因此，如果您需要通过 Java 驱动程序运行此查询，这里是：

    List<Document> documents = collection.aggregate(Arrays.asList(
            new Document("$project", new Document()
                    // include data1
                    .append("data1", 1)
                    // include data2
                    .append("data2", 1)
                    // include only those elements of array1 which match the filter condition
                    .append("array1", new Document("$filter",
                            new Document("input", "$array1")
                                    .append("as", "a")
                                    .append("cond", new Document("$eq", Arrays.asList("$$a.field1", "expectedvalue"))))))
    )).into(new ArrayList<>());