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Today, I will talk to you about how to use cursors in MongoDB. Many people may not know much about it. In order to make you understand better, the editor has summarized the following for you. I hope you can get something according to this article.

What is a cursor?

Cursor is a method of processing data. In order to view or process the data in the result set, the cursor provides the ability to browse the data forward or backward one or more rows at a time.

Cursors are actually a mechanism that can extract one record at a time from a result set that includes multiple data records. A cursor can be seen as a query result set (which can be zero, one, or multiple records retrieved by related selection statements) and a temporary file that points to a specific record in the result set. provides the ability to browse data forward or backward in the query result set and process the data in the result set. With cursors, users can access any row of data in the result set, and after placing the cursor on a row, they can perform operations on that row or on a row block from that location.

2. Cursor of MongoDB

In MongoDB, a cursor is returned using the db.collection.find () method. If we want to access the document, we need to use the iterator of the cursor. However, in mongo shell, if no variable is specified for the returned cursor, the cursor will automatically return the first 20 records first. Let's use a few concrete examples to illustrate how to use cursors.

Define a cursor

Var mycursor = db.emp.find ()

Use cursors to access documents

Var mycursor = db.emp.find () while (mycursor.hasNext ()) {printjson (mycursor.next ())} can also be like this: mycursor.forEach (printjson)

Cursors and arrays

Var mycursor = db.emp.find () define cursors var myarray = mycursor.toArray () convert cursors to an array var myDocument = myarray [3] access documents through array elements

Paged queries: skip and limit

Each page displays 5 records var mycursor = db.emp.find () .limit (5) first page var mycursor = db.emp.find () .limit (5) .skip (5) second page

Close cursors: by default, cursors that are not in use within 10 minutes are automatically closed. You can use .noCursorTimeout () to set the cursor closing option, which requires you to manually close the cursor.

Var mycursor = db.emp.find (). NoCursorTimeout () after reading the above, do you have any further understanding of how to use cursors in MongoDB? If you want to know more knowledge or related content, please follow the industry information channel, thank you for your support.

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