我在聚合查询中使用了$lookup
,但我发现它的作用类似于LEFT OUTER JOIN
。
我想要通过
$lookup
获取精确匹配的文档(INNER JOIN)。
有什么方法可以实现吗?
这是我的inventory
集合:
/* 1 */
{
"_id" : 1,
"sku" : "abc",
"description" : "product 1",
"instock" : 120
}
/* 2 */
{
"_id" : 2,
"sku" : "def",
"description" : "product 2",
"instock" : 80
}
/* 3 */
{
"_id" : 3,
"sku" : "ijk",
"description" : "product 3",
"instock" : 60
}
/* 4 */
{
"_id" : 4,
"sku" : "jkl",
"description" : "product 4",
"instock" : 70
}
/* 5 */
{
"_id" : 5,
"sku" : null,
"description" : "Incomplete"
}
这是我的orders
集合
/* 1 */
{
"_id" : 1,
"item" : "abc",
"price" : 12,
"quantity" : 2
}
/* 2 */
{
"_id" : 2,
"item" : "jkl",
"price" : 20,
"quantity" : 1
}
/* 3 */
{
"_id" : 10,
"item" : "jklw",
"price" : 20,
"quantity" : 1
}
这是一个查询
db.getCollection('inventory').aggregate([
{
$lookup:
{
from: "orders",
localField: "sku",
foreignField: "item",
as: "inventory_docs"
}
}
])
在这个查询中,我会得到所有与orders
文档匹配的inventory
文档。
预期结果
/* 1 */
{
"_id" : 1,
"sku" : "abc",
"description" : "product 1",
"instock" : 120,
"inventory_docs" : [
{
"_id" : 1,
"item" : "abc",
"price" : 12,
"quantity" : 2
}
]
}
/* 2 */
{
"_id" : 4,
"sku" : "jkl",
"description" : "product 4",
"instock" : 70,
"inventory_docs" : [
{
"_id" : 2,
"item" : "jkl",
"price" : 20,
"quantity" : 1
}
]
}