如何从MongoDB中的集合中检索文档？
要从MongoDB中的集合中检索文档，您需要使用find()方法。语法如下：
db.yourCollectionName.find();
上面的语法将返回MongoDB中集合中的所有文档。为了理解上述语法，让我们创建一个包含文档的集合。创建文档的查询如下：
> db.retrieveAllStudents.insertOne({"StudentId":"STUD101","StudentName":"David","StudentAge":24});
{
"acknowledged" : true, "insertedId" : ObjectId("5c6bf5cf68174aae23f5ef4e")
}
> db.retrieveAllStudents.insertOne({"StudentId":"STUD102","StudentName":"Carol","StudentAge":22});
{
"acknowledged" : true, "insertedId" : ObjectId("5c6bf5e968174aae23f5ef4f")
}
> db.retrieveAllStudents.insertOne({"StudentId":"STUD103","StudentName":"Maxwell","StudentAge":25});
{
"acknowledged" : true, "insertedId" : ObjectId("5c6bf5f768174aae23f5ef50")
}
> db.retrieveAllStudents.insertOne({"StudentId":"STUD104","StudentName":"Bob","StudentAge":23});
{
"acknowledged" : true, "insertedId" : ObjectId("5c6bf60868174aae23f5ef51")
}
> db.retrieveAllStudents.insertOne({"StudentId":"STUD105","StudentName":"Sam","StudentAge":27});
{
"acknowledged" : true, "insertedId" : ObjectId("5c6bf61b68174aae23f5ef52")
}现在，您可以使用上述语法来借助find()method来从集合中检索所有文档。查询如下：
> db.retrieveAllStudents.find();
以下是输出：
{ "_id" : ObjectId("5c6bf5cf68174aae23f5ef4e"), "StudentId" : "STUD-101", "StudentName" :
"David", "StudentAge" : 24 }
{ "_id" : ObjectId("5c6bf5e968174aae23f5ef4f"), "StudentId" : "STUD-102", "StudentName" :
"Carol", "StudentAge" : 22 }
{ "_id" : ObjectId("5c6bf5f768174aae23f5ef50"), "StudentId" : "STUD-103", "StudentName" :
"Maxwell", "StudentAge" : 25 }
{ "_id" : ObjectId("5c6bf60868174aae23f5ef51"), "StudentId" : "STUD-104", "StudentName" :
"Bob", "StudentAge" : 23 }
{ "_id" : ObjectId("5c6bf61b68174aae23f5ef52"), "StudentId" : "STUD-105", "StudentName" :
"Sam", "StudentAge" : 27 }要获得正确格式的输出，请pretty()与一起使用find()。查询如下：
> db.retriveAllStudents.find().pretty();
以下是输出：
{
"_id" : ObjectId("5c6bf5cf68174aae23f5ef4e"),
"StudentId" : "STUD-101",
"StudentName" : "David",
"StudentAge" : 24
}
{
"_id" : ObjectId("5c6bf5e968174aae23f5ef4f"),
"StudentId" : "STUD-102",
"StudentName" : "Carol",
"StudentAge" : 22
}
{
"_id" : ObjectId("5c6bf5f768174aae23f5ef50"),
"StudentId" : "STUD-103",
"StudentName" : "Maxwell",
"StudentAge" : 25
}
{
"_id" : ObjectId("5c6bf60868174aae23f5ef51"),
"StudentId" : "STUD-104",
"StudentName" : "Bob",
"StudentAge" : 23
}
{
"_id" : ObjectId("5c6bf61b68174aae23f5ef52"),
"StudentId" : "STUD-105",
"StudentName" : "Sam",
"StudentAge" : 27
}如果要根据某些条件检索单个文档，则可以使用以下查询。在这里，我们正在检索StudentName为“Maxwell”的文档：
> db.retriveAllStudents.find({"StudentName":"Maxwell"}).pretty();以下是输出：
{
"_id" : ObjectId("5c6bf5f768174aae23f5ef50"),
"StudentId" : "STUD-103",
"StudentName" : "Maxwell",
"StudentAge" : 25
}