在MongoDB中索引嵌套字段

Question

我有一个集合，其中包含许多具有此结构的产品文档。每个文档代表一个笛卡尔产品记录，并附带产品价格。

{
        "name": "PRD_SV_HB2_SVH",
        "criterias": [
            {
                "type": "PREMIUM_REGION",
                "value": "COD_RP_KZH"
            },
            {
                "type": "ACCIDENT",
                "value": "COD_UZ_EIN"
            },
            {
                "type": "AGE_GROUP",
                "value": "COD_LA_G36"
            },
            {
                "type": "PRICE_MODEL",
                "value": "COD_TM_HO2"
            },
            {
                "type": "PRICE_TABLE",
                "value": "PRT_SU_HB2_V001_2009010"
            },
            {
                "type": "DEDUCTIBLE",
                "value": "COD_SB_HO4"
            }
        ],
        "price": {
            "pricingElements": {
                "BASE_PRICE": {
                    "currency": "CHF",
                    "amount": 67.8
                }
            }
        },
        "priceType": "STANDARD",
        "_class": "a.b.c.Product"
    }

当查询集合中唯一的笛卡尔积记录时，我使用以下查询：

db.product.find({ "name": "PRD_SV_HB2_SVH", "$and": [
    { "criterias": { "$elemMatch": { "value": "COD_LA_G36" } } }, 
    { "criterias": { "$elemMatch": { "value": "COD_SB_HO4" } } }, 
    { "criterias": { "$elemMatch": { "value": "COD_UZ_EIN" } } }, 
    { "criterias": { "$elemMatch": { "value": "COD_RP_KZH" } } }, 
    { "criterias": { "$elemMatch": { "value": "COD_TM_HO2" } } }, 
    { "criterias": { "$elemMatch": { "value": "PRT_SU_HB2_V001_2009010" } } }
    ] 
})

查询花费了超过2秒钟的时间才能产生不令人满意的结果。当我在同一查询上运行explain时，我可以看到MongoDB使用索引name，但没有为此查询使用专用索引name_value。

{
    "queryPlanner" : {
        "plannerVersion" : 1,
        "namespace" : "productEngine.product",
        "indexFilterSet" : false,
        "parsedQuery" : {
            "$and" : [
                {
                    "criterias" : {
                        "$elemMatch" : {
                            "value" : {
                                "$eq" : "COD_LA_G36"
                            }
                        }
                    }
                },
                {
                    "criterias" : {
                        "$elemMatch" : {
                            "value" : {
                                "$eq" : "COD_SB_HO4"
                            }
                        }
                    }
                },
                {
                    "criterias" : {
                        "$elemMatch" : {
                            "value" : {
                                "$eq" : "COD_UZ_EIN"
                            }
                        }
                    }
                },
                {
                    "criterias" : {
                        "$elemMatch" : {
                            "value" : {
                                "$eq" : "COD_RP_KZH"
                            }
                        }
                    }
                },
                {
                    "criterias" : {
                        "$elemMatch" : {
                            "value" : {
                                "$eq" : "COD_TM_HO2"
                            }
                        }
                    }
                },
                {
                    "criterias" : {
                        "$elemMatch" : {
                            "value" : {
                                "$eq" : "PRT_SU_HB2_V001_2009010"
                            }
                        }
                    }
                },
                {
                    "name" : {
                        "$eq" : "PRD_SV_HB2_SVH"
                    }
                }
            ]
        },
        "winningPlan" : {
            "stage" : "FETCH",
            "filter" : {
                "$and" : [
                    {
                        "criterias" : {
                            "$elemMatch" : {
                                "value" : {
                                    "$eq" : "COD_LA_G36"
                                }
                            }
                        }
                    },
                    {
                        "criterias" : {
                            "$elemMatch" : {
                                "value" : {
                                    "$eq" : "COD_SB_HO4"
                                }
                            }
                        }
                    },
                    {
                        "criterias" : {
                            "$elemMatch" : {
                                "value" : {
                                    "$eq" : "COD_UZ_EIN"
                                }
                            }
                        }
                    },
                    {
                        "criterias" : {
                            "$elemMatch" : {
                                "value" : {
                                    "$eq" : "COD_RP_KZH"
                                }
                            }
                        }
                    },
                    {
                        "criterias" : {
                            "$elemMatch" : {
                                "value" : {
                                    "$eq" : "COD_TM_HO2"
                                }
                            }
                        }
                    },
                    {
                        "criterias" : {
                            "$elemMatch" : {
                                "value" : {
                                    "$eq" : "PRT_SU_HB2_V001_2009010"
                                }
                            }
                        }
                    }
                ]
            },
            "inputStage" : {
                "stage" : "IXSCAN",
                "keyPattern" : {
                    "name" : 1
                },
                "indexName" : "name",
                "isMultiKey" : false,
                "multiKeyPaths" : {
                    "name" : [ ]
                },
                "isUnique" : false,
                "isSparse" : false,
                "isPartial" : false,
                "indexVersion" : 2,
                "direction" : "forward",
                "indexBounds" : {
                    "name" : [
                        "[\"PRD_SV_HB2_SVH\", \"PRD_SV_HB2_SVH\"]"
                    ]
                }
            }
        },
        "rejectedPlans" : [
            {
                "stage" : "FETCH",
                "filter" : {
                    "$and" : [
                        {
                            "criterias" : {
                                "$elemMatch" : {
                                    "value" : {
                                        "$eq" : "COD_LA_G36"
                                    }
                                }
                            }
                        },
                        {
                            "criterias" : {
                                "$elemMatch" : {
                                    "value" : {
                                        "$eq" : "COD_SB_HO4"
                                    }
                                }
                            }
                        },
                        {
                            "criterias" : {
                                "$elemMatch" : {
                                    "value" : {
                                        "$eq" : "COD_UZ_EIN"
                                    }
                                }
                            }
                        },
                        {
                            "criterias" : {
                                "$elemMatch" : {
                                    "value" : {
                                        "$eq" : "COD_RP_KZH"
                                    }
                                }
                            }
                        },
                        {
                            "criterias" : {
                                "$elemMatch" : {
                                    "value" : {
                                        "$eq" : "COD_TM_HO2"
                                    }
                                }
                            }
                        },
                        {
                            "criterias" : {
                                "$elemMatch" : {
                                    "value" : {
                                        "$eq" : "PRT_SU_HB2_V001_2009010"
                                    }
                                }
                            }
                        }
                    ]
                },
                "inputStage" : {
                    "stage" : "IXSCAN",
                    "keyPattern" : {
                        "name" : 1,
                        "criteria.value" : 1
                    },
                    "indexName" : "name_value",
                    "isMultiKey" : false,
                    "multiKeyPaths" : {
                        "name" : [ ],
                        "criteria.value" : [ ]
                    },
                    "isUnique" : false,
                    "isSparse" : false,
                    "isPartial" : false,
                    "indexVersion" : 2,
                    "direction" : "forward",
                    "indexBounds" : {
                        "name" : [
                            "[\"PRD_SV_HB2_SVH\", \"PRD_SV_HB2_SVH\"]"
                        ],
                        "criteria.value" : [
                            "[MinKey, MaxKey]"
                        ]
                    }
                }
            },
            {
                "stage" : "FETCH",
                "filter" : {
                    "$and" : [
                        {
                            "criterias" : {
                                "$elemMatch" : {
                                    "value" : {
                                        "$eq" : "COD_LA_G36"
                                    }
                                }
                            }
                        },
                        {
                            "criterias" : {
                                "$elemMatch" : {
                                    "value" : {
                                        "$eq" : "COD_SB_HO4"
                                    }
                                }
                            }
                        },
                        {
                            "criterias" : {
                                "$elemMatch" : {
                                    "value" : {
                                        "$eq" : "COD_UZ_EIN"
                                    }
                                }
                            }
                        },
                        {
                            "criterias" : {
                                "$elemMatch" : {
                                    "value" : {
                                        "$eq" : "COD_RP_KZH"
                                    }
                                }
                            }
                        },
                        {
                            "criterias" : {
                                "$elemMatch" : {
                                    "value" : {
                                        "$eq" : "COD_TM_HO2"
                                    }
                                }
                            }
                        },
                        {
                            "criterias" : {
                                "$elemMatch" : {
                                    "value" : {
                                        "$eq" : "PRT_SU_HB2_V001_2009010"
                                    }
                                }
                            }
                        }
                    ]
                },
                "inputStage" : {
                    "stage" : "IXSCAN",
                    "keyPattern" : {
                        "name" : 1,
                        "priceType" : 1,
                        "criteria.value" : 1
                    },
                    "indexName" : "name_priceType_value",
                    "isMultiKey" : false,
                    "multiKeyPaths" : {
                        "name" : [ ],
                        "priceType" : [ ],
                        "criteria.value" : [ ]
                    },
                    "isUnique" : false,
                    "isSparse" : false,
                    "isPartial" : false,
                    "indexVersion" : 2,
                    "direction" : "forward",
                    "indexBounds" : {
                        "name" : [
                            "[\"PRD_SV_HB2_SVH\", \"PRD_SV_HB2_SVH\"]"
                        ],
                        "priceType" : [
                            "[MinKey, MaxKey]"
                        ],
                        "criteria.value" : [
                            "[MinKey, MaxKey]"
                        ]
                    }
                }
            }
        ]
    },
    "serverInfo" : {
        "host" : "1a63040d1b73",
        "port" : 27018,
        "version" : "3.4.10",
        "gitVersion" : "078f28920cb24de0dd479b5ea6c66c644f6326e9"
    },
    "ok" : 1
}

我目前这样创建name_value复合索引：

{"name":1, "criteria.value":1}

这是在嵌套文档字段上创建复合索引的正确方法，还是我在这里遗漏了什么？为什么不使用name_value索引？