有一个文档，里面包含一个子文档，大体如下：

{
    "_id" : ObjectId("59376b35a233be856d4a0731"),
    "plate_number" : "京A11111",
    "breakdown" : [
        {
            "file_id" : "4003732",
            "case_number" : "xxxx",
            "lev_code" : "B231",
            "crdate" : ISODate("2016-01-19T17:00:43Z")
        },
        {
            "file_id" : "4010523",
            "case_number" : "xxxx",
            "lev_code" : "B231",
            "crdate" : ISODate("2016-06-29T14:53:36Z")
        },
        {
            "file_id" : "4010980",
            "case_number" : "xxxx",
            "lev_code" : "B211",
            "crdate" : ISODate("2016-07-01T17:18:40Z")
        }
    ]
}

现在的需求是，如何使用PHP 7根据plate_number & lev_code查询匹配的个数

还有个问题是，如何能匹配符合条件的子文档？

# mongo
find({plate_number:"京A11111", breakdown.lev_code:"B231"})
{
    "breakdown" : [
        {
            "file_id" : "4003732",
            "case_number" : "xxxx",
            "lev_code" : "B231",
            "crdate" : ISODate("2016-01-19T17:00:43Z")
        },
        {
            "file_id" : "4010523",
            "case_number" : "xxxx",
            "lev_code" : "B231",
            "crdate" : ISODate("2016-06-29T14:53:36Z")
        },
        {
            "file_id" : "4010980",
            "case_number" : "xxxx",
            "lev_code" : "B211",
            "crdate" : ISODate("2016-07-01T17:18:40Z")
        }
    ]
}