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7e55b542
编写于
11月 29, 2021
作者:
雪洛
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docs: update embed lookup
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@@ -3410,6 +3410,101 @@ let res = await db.collection('orders').aggregate()
]
```
**多表联表查询**
假设
`orders`
集合有以下记录:
```
js
[
{
"
_id
"
:
4
,
"
book
"
:
"
book1
"
,
"
price
"
:
30
,
"
quantity
"
:
2
},
{
"
_id
"
:
5
,
"
book
"
:
"
book2
"
,
"
price
"
:
20
,
"
quantity
"
:
1
}
]
```
`books`
集合有以下记录:
```
js
[
{
"
_id
"
:
"
book1
"
,
"
author
"
:
"
author1
"
,
"
title
"
:
"
novel 1
"
},
{
"
_id
"
:
"
book2
"
,
"
author
"
:
"
author2
"
,
"
title
"
:
"
science 1
"
},
]
```
`authors`
集合有以下记录:
```
js
[
{
"
_id
"
:
"
author1
"
,
"
name
"
:
"
A1
"
},
{
"
_id
"
:
"
author2
"
,
"
author
"
:
"
A2
"
}
]
```
如需orders关联books,book再关联authors查询,可以在pipeline内再使用lookup
```
js
const
db
=
cloud
.
database
()
const
$
=
db
.
command
.
aggregate
let
res
=
await
db
.
collection
(
'
orders
'
).
aggregate
()
.
lookup
({
from
:
'
books
'
,
let
:
{
book_id
:
'
$book
'
},
pipeline
:
$
.
pipeline
()
.
match
(
$
.
expr
(
$
.
eq
([
'
$_id
'
,
'
$$book_id
'
]))
)
.
lookup
({
from
:
'
authors
'
,
let
:
{
author_id
:
'
$author
'
},
pipeline
:
$
.
pipeline
()
.
match
(
$
.
expr
(
$
.
eq
([
'
$_id
'
,
'
$$author_id
'
]))
)
.
done
(),
as
:
'
authorList
'
})
.
done
(),
as
:
'
bookList
'
,
})
.
end
()
```
结果如下
```
js
[
{
"
_id
"
:
4
,
"
book
"
:
"
book1
"
,
"
price
"
:
30
,
"
quantity
"
:
2
,
"
bookList
"
:
[{
"
_id
"
:
"
book1
"
,
"
author
"
:
"
author1
"
,
"
title
"
:
"
novel 1
"
,
authorList
:
[{
"
_id
"
:
"
author1
"
,
"
name
"
:
"
A1
"
}]
}]
},
{
"
_id
"
:
5
,
"
book
"
:
"
book2
"
,
"
price
"
:
20
,
"
quantity
"
:
1
,
"
bookList
"
:
[{
"
_id
"
:
"
book2
"
,
"
author
"
:
"
author2
"
,
"
title
"
:
"
science 1
"
,
authorList
:
[{
"
_id
"
:
"
author2
"
,
"
name
"
:
"
A2
"
}]
}]
}
]
```
### match@aggregate-match
聚合阶段。根据条件过滤文档,并且把符合条件的文档传递给下一个流水线阶段。
...
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