在创建了自己的聚合管道之后，我得出了以下结果：
[
{
"_id": "53712c7238b8d900008ef71c",
"address": [
{
"_id": "53712c7238b8d900008ef71b",
"phoneNumber": "4092348294",
...
}
],
"name": "TestDealer",
"vehicles": [
{
"_id": "53712fa138b8d900008ef720",
"createdAt": "2014-05-12T20:08:00.000Z",
"tags": [
"vehicle"
],
"opts": [
{
"_id": "53712fa138b8d900008ef71e",
"hasSunroof": false,
...
}
],
"listed": true,
"disclosures": [
{
"_id": "53712fa138b8d900008ef71f",
"waterDamage": false,
...
}
],
"details": [
{
"_id": "53712fa138b8d900008ef71d",
"year": 2007,
...
}
]
},
{
"_id": "5373c6439058859af7904a17",
"createdAt": "2014-05-14T19:17:00.000Z",
"tags": [
"vehicle"
],
"opts": [
{
"_id": "5373c6439058859af7904a15",
"hasSunroof": false,
....
"other": []
}
],
"listed": true,
"disclosures": [
{
"_id": "5373c6439058859af7904a16",
"waterDamage": false,
...
}
],
"details": [
{
"_id": "5373c6439058859af7904a14",
"year": 2013,
...
}
]
}
]
}
]
如您所见，vehicles是一系列遵循特定架构的子文档（车辆）：
details subdocs opts subdocs disclosures subdocs 对于details，disclosures和opts中的每一个，我想返回数组中的第一个子数据块而不是数组。但是，我不知道从哪里开始。我不能真正放松车辆，因为它可能是空的。
以下是我的最终数据：
[
{
"_id": "53712c7238b8d900008ef71c",
"address": [
{
"_id": "53712c7238b8d900008ef71b",
"phoneNumber": "4092348294",
...
}
],
"name": "TestDealer",
"vehicles": [
{
"_id": "53712fa138b8d900008ef720",
"createdAt": "2014-05-12T20:08:00.000Z",
"tags": [
"vehicle"
],
"opts": {
"_id": "53712fa138b8d900008ef71e",
"hasSunroof": false,
...
},
"listed": true,
"disclosures": {
"_id": "53712fa138b8d900008ef71f",
"waterDamage": false,
...
},
"details": {
"_id": "53712fa138b8d900008ef71d",
"year": 2007,
...
}
},
{
"_id": "5373c6439058859af7904a17",
"createdAt": "2014-05-14T19:17:00.000Z",
"tags": [
"vehicle"
],
"opts": {
"_id": "5373c6439058859af7904a15",
"hasSunroof": false,
....
"other": []
},
"listed": true,
"disclosures": {
"_id": "5373c6439058859af7904a16",
"waterDamage": false,
...
},
"details": {
"_id": "5373c6439058859af7904a14",
"year": 2013,
...
}
}
]
}
]
修改
以下是我获取数据的聚合（在CoffeeScript中）：
{
$match:
_id: ObjectId(params.id)
}
{
$unwind: '$inventories'
}
{
$match:
'inventories._id': 'active'
}
{
$redact:
$cond:
if:
$eq:['$listed',false]
then: '$$PRUNE'
else: '$$DESCEND'
}
{
$project:
address: 1
name: '$dealerName'
email: '$_id.email'
vehicles: '$inventories.vehicles'
}
以及原始数据：
{ "_id" : ObjectId( "53712c7238b8d900008ef71c" ),
"email" : "test@test.com",
"createdAt" : Date( 1399925280000 ),
"password" : "$2a$10$3dhicJuONkXeI9mQflXF0.JftAx7mLQaY2./6a3O7xdrs5qfH2zMW",
"firstName" : "TestName",
"lastName" : "testName",
"dealerName" : "TestDealer",
"dealerType" : "Franchised Dealer",
"emailIsVerified" : false,
"lastLoggedInAt" : Date( 1400247300000 ),
"expiresAt" : Date( 4524062882000 ),
"deletedAt" : null,
"updatedAt" : Date( 1400251500000 ),
"inventories" : [
{ "title" : "activeInventory",
"_id" : "active",
"vehicles" : [
{ "_id" : ObjectId( "53712fa138b8d900008ef720" ),
"createdAt" : Date( 1399925280000 ),
"tags" : [
"vehicle" ],
"opts" : [
{ "_id" : ObjectId( "53712fa138b8d900008ef71e" ),
"hasSunroof" : false,
"hasSnowTires" : false,
"hasPowerWindows" : false,
"hasNavigationSystem" : false,
"hasManuals" : false,
"hasMags" : false,
"hasLeather" : false,
"hasKeylessEntry" : false,
"hasHeatedSeats" : false,
"hasDvdSystem" : false,
"hasAirConditioning" : false,
"has2SetsOfKeys" : false,
"other" : [] } ],
"listed" : true,
"disclosures" : [
{ "_id" : ObjectId( "53712fa138b8d900008ef71f" ),
"waterDamage" : false,
"vehicleLien" : false,
"usVehicle" : false,
"totalLossByInsurer" : false,
"theftOrRecovery" : false,
"taxiOrLimo" : false,
"structuralPartsAreDamagedOrAlteredOrRepaired" : false,
"suspensionOrSubFrameNeedsRepair" : false,
"repainted" : false,
"previousDamageExceeding3k" : false,
"powerTrainNeedsRepair" : false,
"policeCruiser" : false,
"outOfProvinceOrState" : false,
"originalOwner" : false,
"originalManufacturerVinPlate" : false,
"originalSpecificationsChanged" : false,
"odometerRolledBackOrReplaced" : false,
"manufacturerWarrantyCancelled" : false,
"manufacturerBadgesChanged" : false,
"fuelSystemNeedsRepair" : false,
"fireDamage" : false,
"engineNeedsRepair" : false,
"emergencyVehicle" : false,
"electricalSystemNeedsRepair" : false,
"dailyRental" : false,
"computerNeedsRepair" : false,
"antiLockBrakesDamagedOrInoperable" : false,
"airbagIsMissingOrInoperable" : false,
"airConditioningNeedsRepair" : false } ],
"details" : [
{ "_id" : ObjectId( "53712fa138b8d900008ef71d" ),
"year" : 2007,
"vin" : "JN8AZ08W27W649264",
"trim" : "SE",
"transmission" : "Automatic",
"price" : 132123,
"model" : "Murano 4D Utility AWD",
"mileageReading" : 125000,
"make" : "Nissan",
"interiorColor" : "Black",
"history" : "Carproof Verified ($40.00)",
"hasAccident" : false,
"fuelType" : "Biodiesel",
"exteriorColor" : "Blue",
"driveTrain" : "FWD",
"description" : "dsadas",
"cylinders" : 4,
"mileageType" : "kms" } ] },
{ "_id" : ObjectId( "53713bfc1429925f0faf79d0" ),
"createdAt" : Date( 1399929780000 ),
"tags" : [
"vehicle" ],
"opts" : [
{ "_id" : ObjectId( "53713bfc1429925f0faf79ce" ),
"hasSunroof" : false,
"hasSnowTires" : false,
"hasPowerWindows" : false,
"hasNavigationSystem" : false,
"hasManuals" : false,
"hasMags" : false,
"hasLeather" : false,
"hasKeylessEntry" : false,
"hasHeatedSeats" : false,
"hasDvdSystem" : false,
"hasAirConditioning" : false,
"has2SetsOfKeys" : false,
"other" : [] } ],
"listed" : false,
"disclosures" : [
{ "_id" : ObjectId( "53713bfc1429925f0faf79cf" ),
"waterDamage" : false,
"vehicleLien" : false,
"usVehicle" : false,
"totalLossByInsurer" : false,
"theftOrRecovery" : false,
"taxiOrLimo" : false,
"structuralPartsAreDamagedOrAlteredOrRepaired" : false,
"suspensionOrSubFrameNeedsRepair" : false,
"repainted" : false,
"previousDamageExceeding3k" : false,
"powerTrainNeedsRepair" : false,
"policeCruiser" : false,
"outOfProvinceOrState" : false,
"originalOwner" : false,
"originalManufacturerVinPlate" : false,
"originalSpecificationsChanged" : false,
"odometerRolledBackOrReplaced" : false,
"manufacturerWarrantyCancelled" : false,
"manufacturerBadgesChanged" : false,
"fuelSystemNeedsRepair" : false,
"fireDamage" : false,
"engineNeedsRepair" : false,
"emergencyVehicle" : false,
"electricalSystemNeedsRepair" : false,
"dailyRental" : false,
"computerNeedsRepair" : false,
"antiLockBrakesDamagedOrInoperable" : false,
"airbagIsMissingOrInoperable" : false,
"airConditioningNeedsRepair" : false } ],
"details" : [
{ "_id" : ObjectId( "53713bfc1429925f0faf79cd" ),
"year" : 2007,
"vin" : "JN8AZ08W27W649264",
"trim" : "SE",
"transmission" : "Manual",
"price" : 13241234,
"model" : "Murano 4D Utility AWD",
"mileageReading" : 1312312,
"make" : "Mercedes-Benz",
"interiorColor" : "Black",
"history" : "Carproof Claims ($25.00)",
"hasAccident" : true,
"fuelType" : "Diesel",
"exteriorColor" : "Black",
"driveTrain" : "RWD",
"description" : "werwe",
"cylinders" : 4,
"mileageType" : "kms" } ] },
{ "_id" : ObjectId( "5373c6439058859af7904a17" ),
"createdAt" : Date( 1400095020000 ),
"tags" : [
"vehicle" ],
"opts" : [
{ "_id" : ObjectId( "5373c6439058859af7904a15" ),
"hasSunroof" : false,
"hasSnowTires" : false,
"hasPowerWindows" : false,
"hasNavigationSystem" : false,
"hasManuals" : false,
"hasMags" : false,
"hasLeather" : false,
"hasKeylessEntry" : false,
"hasHeatedSeats" : false,
"hasDvdSystem" : false,
"hasAirConditioning" : false,
"has2SetsOfKeys" : false,
"other" : [] } ],
"listed" : true,
"disclosures" : [
{ "_id" : ObjectId( "5373c6439058859af7904a16" ),
"waterDamage" : false,
"vehicleLien" : false,
"usVehicle" : false,
"totalLossByInsurer" : false,
"theftOrRecovery" : false,
"taxiOrLimo" : false,
"structuralPartsAreDamagedOrAlteredOrRepaired" : false,
"suspensionOrSubFrameNeedsRepair" : false,
"repainted" : false,
"previousDamageExceeding3k" : false,
"powerTrainNeedsRepair" : false,
"policeCruiser" : false,
"outOfProvinceOrState" : false,
"originalOwner" : false,
"originalManufacturerVinPlate" : false,
"originalSpecificationsChanged" : false,
"odometerRolledBackOrReplaced" : false,
"manufacturerWarrantyCancelled" : false,
"manufacturerBadgesChanged" : false,
"fuelSystemNeedsRepair" : false,
"fireDamage" : false,
"engineNeedsRepair" : false,
"emergencyVehicle" : false,
"electricalSystemNeedsRepair" : false,
"dailyRental" : false,
"computerNeedsRepair" : false,
"antiLockBrakesDamagedOrInoperable" : false,
"airbagIsMissingOrInoperable" : false,
"airConditioningNeedsRepair" : false } ],
"details" : [
{ "_id" : ObjectId( "5373c6439058859af7904a14" ),
"year" : 2013,
"vin" : "12345678901234567",
"trim" : "SE",
"transmission" : "Automatic",
"price" : 13564,
"model" : "Red",
"mileageReading" : 13453,
"make" : "Daihatsu",
"interiorColor" : "Black",
"history" : "Carproof Verified ($40.00)",
"hasAccident" : true,
"fuelType" : "Diesel",
"exteriorColor" : "Black",
"driveTrain" : "FWD",
"description" : "wrw",
"cylinders" : 3,
"mileageType" : "kms" } ] } ],
"tags" : [
"inventory",
"active",
"vehicles" ] },
{ "title" : "soldInventory",
"_id" : "sold",
"vehicles" : [],
"tags" : [
"inventory",
"sold",
"vehicles" ] },
{ "title" : "deletedInventory",
"_id" : "deleted",
"vehicles" : [],
"tags" : [
"inventory",
"deleted",
"vehicles" ] } ],
"address" : [
{ "_id" : ObjectId( "53712c7238b8d900008ef71b" ),
"phoneNumber" : "4092348294",
"country" : "Canada",
"zip" : "301111",
"region" : "Quebec",
"city" : "Montreal",
"street2" : "Apt. 101",
"street1" : "1213 Street",
"additionalNumbers" : [] } ],
"__v" : 3 }
答案 0 :(得分：1)
如果你使用2.6（你必须使用$ redact），并且如果没有标签或opts，如果数组总是保证为空，你可以使用这种技术确保你不会丢失$unwind：
在$project阶段，为您要展开的所有数组添加以下内容以保留第一个元素：
opts:{$cond:{if:{$eq:[{$size:"$opts"},0]}, then:{$literal:[ "none" ]}, else:"$opts"}}
对于每个子阵列，您现在可以对第一个子阵列进行分组，然后再次为下一个子阵列重复。
你需要小心分别对每个阵列进行展开和重新分组以防止任何重复，如果你没有聚合其他东西，你可以在一个组中用尽可能多的$ unwinds进行因为有子阵列。