如何在MongoDB中執(zhí)行SQL Join等效項(xiàng)？如何在MongoDB中執(zhí)行SQL Join等效項(xiàng)？例如，假設(shè)你有兩個集合（用戶和評論），我想用pid = 444以及每個集合的用戶信息來提取所有評論。comments { uid:12345, pid:444, comment="blah" }
{ uid:12345, pid:888, comment="asdf" }
{ uid:99999, pid:444, comment="qwer" }users { uid:12345, name:"john" }
{ uid:99999, name:"mia" }有沒有辦法用一個字段拉出所有評論（例如......查找（{pid：444}））以及與每個評論相關(guān)的用戶信息？目前，我首先得到符合我標(biāo)準(zhǔn)的注釋，然后找出該結(jié)果集中的所有uid，獲取用戶對象，并將它們與注釋的結(jié)果合并。好像我做錯了。
4 回答
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TA貢獻(xiàn)1942條經(jīng)驗(yàn) 獲得超3個贊
我們可以使用mongodb客戶端控制臺將只有一行的簡單函數(shù)合并/加入一個集合中的所有數(shù)據(jù)，現(xiàn)在我們可以執(zhí)行所需的查詢。下面是一個完整的例子
.-作者：
db.authors.insert([
{
_id: 'a1',
name: { first: 'orlando', last: 'becerra' },
age: 27
},
{
_id: 'a2',
name: { first: 'mayra', last: 'sanchez' },
age: 21
}]);.-分類：
db.categories.insert([
{
_id: 'c1',
name: 'sci-fi'
},
{
_id: 'c2',
name: 'romance'
}]);.-書籍
db.books.insert([
{
_id: 'b1',
name: 'Groovy Book',
category: 'c1',
authors: ['a1']
},
{
_id: 'b2',
name: 'Java Book',
category: 'c2',
authors: ['a1','a2']
},]);.-圖書借閱
db.lendings.insert([
{
_id: 'l1',
book: 'b1',
date: new Date('01/01/11'),
lendingBy: 'jose'
},
{
_id: 'l2',
book: 'b1',
date: new Date('02/02/12'),
lendingBy: 'maria'
}]);。- 魔法：
db.books.find().forEach(
function (newBook) {
newBook.category = db.categories.findOne( { "_id": newBook.category } );
newBook.lendings = db.lendings.find( { "book": newBook._id } ).toArray();
newBook.authors = db.authors.find( { "_id": { $in: newBook.authors } } ).toArray();
db.booksReloaded.insert(newBook);
});.-獲取新的收集數(shù)據(jù)：
db.booksReloaded.find().pretty()
.-回應(yīng):)
{
"_id" : "b1",
"name" : "Groovy Book",
"category" : {
"_id" : "c1",
"name" : "sci-fi"
},
"authors" : [
{
"_id" : "a1",
"name" : {
"first" : "orlando",
"last" : "becerra"
},
"age" : 27
}
],
"lendings" : [
{
"_id" : "l1",
"book" : "b1",
"date" : ISODate("2011-01-01T00:00:00Z"),
"lendingBy" : "jose"
},
{
"_id" : "l2",
"book" : "b1",
"date" : ISODate("2012-02-02T00:00:00Z"),
"lendingBy" : "maria"
}
]}{
"_id" : "b2",
"name" : "Java Book",
"category" : {
"_id" : "c2",
"name" : "romance"
},
"authors" : [
{
"_id" : "a1",
"name" : {
"first" : "orlando",
"last" : "becerra"
},
"age" : 27
},
{
"_id" : "a2",
"name" : {
"first" : "mayra",
"last" : "sanchez"
},
"age" : 21
}
],
"lendings" : [ ]}我希望這條線可以幫到你。
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