您可以使用下列語法從collection.find()傳回特定欄位。
情況1 - 語法如下 -
db.yourCollectionName.find({},{"yourFieldName":1}).pretty();上面的欄位名稱設為 1 表示它將只傳回該欄位。如果設為 0，它將傳回除設定為 0 的欄位之外的所有欄位。
情況 2 - 語法如下 -
db.yourCollectionName.find({},{"yourFieldName":0}).pretty();為了理解上述語法，讓我們用 document 建立一個集合。使用文件建立集合的查詢如下 -
> db.returnFieldInFindDemo.insertOne({"StudentName":"John","StudentAge":23,"TechnicalSubject":["MongoDB","MySQL"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c8ebfe72f684a30fbdfd566")
}
> db.returnFieldInFindDemo.insertOne({"StudentName":"Mike","StudentAge":24,"TechnicalSubject":["Java","Python"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c8ebffd2f684a30fbdfd567")
}
> db.returnFieldInFindDemo.insertOne({"StudentName":"Sam","StudentAge":22,"TechnicalSubject":["C","C++"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c8ec00f2f684a30fbdfd568")
}
> db.returnFieldInFindDemo.insertOne({"StudentName":"Carol","StudentAge":20,"TechnicalSubject":["DataStructure","Algorithm"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c8ec0292f684a30fbdfd569")
}借助 find() 方法顯示集合中的所有文件。查詢如下 -
> db.returnFieldInFindDemo.find().pretty();
以下是輸出 -
{
"_id" : ObjectId("5c8ebfe72f684a30fbdfd566"),
"StudentName" : "John",
"StudentAge" : 23,
"TechnicalSubject" : [
"MongoDB",
"MySQL"
]
}
{
"_id" : ObjectId("5c8ebffd2f684a30fbdfd567"),
"StudentName" : "Mike",
"StudentAge" : 24,
"TechnicalSubject" : [
"Java",
"Python"
]
}
{
"_id" : ObjectId("5c8ec00f2f684a30fbdfd568"),
"StudentName" : "Sam",
"StudentAge" : 22,
"TechnicalSubject" : [
"C",
"C++"
]
}
{
"_id" : ObjectId("5c8ec0292f684a30fbdfd569"),
"StudentName" : "Carol",
"StudentAge" : 20,
"TechnicalSubject" : [
"DataStructure",
"Algorithm"
]
}情況 1 - 這是您將傳回特定欄位的查詢。
查詢如下 -
> db.returnFieldInFindDemo.find().pretty();
輸出：
{
"_id" : ObjectId("5c8ebfe72f684a30fbdfd566"),
"StudentName" : "John",
"StudentAge" : 23,
"TechnicalSubject" : [
"MongoDB",
"MySQL"
]
}
{
"_id" : ObjectId("5c8ebffd2f684a30fbdfd567"),
"StudentName" : "Mike",
"StudentAge" : 24,
"TechnicalSubject" : [
"Java",
"Python"
]
}
{
"_id" : ObjectId("5c8ec00f2f684a30fbdfd568"),
"StudentName" : "Sam",
"StudentAge" : 22,
"TechnicalSubject" : [
"C",
"C++"
]
}
{
"_id" : ObjectId("5c8ec0292f684a30fbdfd569"),
"StudentName" : "Carol",
"StudentAge" : 20,
"TechnicalSubject" : [
"DataStructure",
"Algorithm"
]
}看看上面的範例輸出，我已將「TechnicalSubject」欄位初始化為 1。這意味著它將僅從所有文件中返回“TechnicalSubject”欄位。
情況2
情況2
strong> - 在第二種情況下，如果將「TechnicalSubject」欄位設為0，則表示您將取得除“TechnicalSubject”之外的所有欄位。查詢如下-
> db.retunFieldInFindDemo.find({},{"TechnicalSubject":0}).pretty();以下是輸出：
{
"_id" : ObjectId("5c8ebfe72f684a30fbdfd566"),
"StudentName" : "John",
"StudentAge" : 23
}
{
"_id" : ObjectId("5c8ebffd2f684a30fbdfd567"),
"StudentName" : "Mike",
"StudentAge" : 24
}
{
"_id" : ObjectId("5c8ec00f2f684a30fbdfd568"),
"StudentName" : "Sam",
"StudentAge" : 22
}
{
"_id" : ObjectId("5c8ec0292f684a30fbdfd569"),
"StudentName" : "Carol",
"StudentAge" : 20
}情況3 - 如您所知，如果您只使用find() 那麼它會傳回所有欄位。
查詢如下 -
> db.retunFieldInFindDemo.find();
以下是輸出：
{ "_id" : ObjectId("5c8ebfe72f684a30fbdfd566"), "StudentName" : "John", "StudentAge" : 23, "TechnicalSubject" : [ "MongoDB", "MySQL" ] }
{ "_id" : ObjectId("5c8ebffd2f684a30fbdfd567"), "StudentName" : "Mike", "StudentAge" : 24, "TechnicalSubject" : [ "Java", "Python" ] }
{ "_id" : ObjectId("5c8ec00f2f684a30fbdfd568"), "StudentName" : "Sam", "StudentAge" : 22, "TechnicalSubject" : [ "C", "C++" ] }
{ "_id" : ObjectId("5c8ec0292f684a30fbdfd569"), "StudentName" : "Carol", "StudentAge" : 20, "TechnicalSubject" : [ "DataStructure", "Algorithm" ] }以上是collection.find() 總是傳回 MongoDB 的所有欄位？的詳細內容。更多資訊請關注PHP中文網其他相關文章！
