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法學如何在 MongoDB 中獲取特定欄位作為結果？
要獲取 MongoDB 中的某個欄位作為結果，你可以使用 findOne()。以下為語法：-
db.yourCollectionName.findOne({"yourFieldName1":yourValue},{yourFieldName2:1});讓我們先用文件建立一個集合：-
> db.particularFieldDemo.insertOne({"EmployeeName":"John Smith","EmployeeAge":26,"EmployeeTechnology":"MongoDB"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd9b4abb50a6c6dd317ada2")
}
> db.particularFieldDemo.insertOne({"EmployeeName":"Chris Brown","EmployeeAge":28,"EmployeeTechnology":"Java"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd9b4d2b50a6c6dd317ada3")
}
> db.particularFieldDemo.insertOne({"EmployeeName":"David Miller","EmployeeAge":30,"EmployeeTechnology":"MySQL"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd9b4e8b50a6c6dd317ada4")
}
> db.particularFieldDemo.insertOne({"EmployeeName":"John Doe","EmployeeAge":31,"EmployeeTechnology":"C++"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd9b527b50a6c6dd317ada5")
}以下為使用 find() 方法在集合中顯示所有文件的查詢：-
> db.particularFieldDemo.find().pretty();
這將生成如下的輸出：-
{
"_id" : ObjectId("5cd9b4abb50a6c6dd317ada2"),
"EmployeeName" : "John Smith",
"EmployeeAge" : 26,
"EmployeeTechnology" : "MongoDB"
}
{
"_id" : ObjectId("5cd9b4d2b50a6c6dd317ada3"),
"EmployeeName" : "Chris Brown",
"EmployeeAge" : 28,
"EmployeeTechnology" : "Java"
}
{
"_id" : ObjectId("5cd9b4e8b50a6c6dd317ada4"),
"EmployeeName" : "David Miller",
"EmployeeAge" : 30,
"EmployeeTechnology" : "MySQL"
}
{
"_id" : ObjectId("5cd9b527b50a6c6dd317ada5"),
"EmployeeName" : "John Doe",
"EmployeeAge" : 31,
"EmployeeTechnology" : "C++"
}以下為在 MongoDB 中查詢某個欄位作為結果的查詢：-
> db.particularFieldDemo.findOne({"EmployeeTechnology":"Java"},{EmployeeName:1});這將生成如下的輸出：-
{
"_id" : ObjectId("5cd9b4d2b50a6c6dd317ada3"),
"EmployeeName" : "Chris Brown"
}
更新於： 2019 年 7 月 30 日
98 次瀏覽
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