Cloud Firestore、nodejs（云函数）、同步访问

Question

What is the Java equivalent of 'synchronize' in Firestore, nodejs (cloud functions)?

Suppose I keep a counter in the db and I want to increment it by 1, so I have to read the value, increment it, and store it back.

How do I make sure the counter value didn't change by other party, between the read and write action?

Answer 1

How do I make sure the counter value didn't change by other party, between the read and write action?

There are two ways in which you can solve this problem.

The first one would be to use a transaction , which is an operation where you read a value from a document, you increment it and then write the document back.

The second solution would be to use the FieldValue.increment(50) operator:

An increment operation increases or decreases the current value of a field by the given amount. If the field does not exist or if the current field value is not a numeric value, the operation sets the field to the given value.

If you need at some point in time to decrement a value, simply pass a negative value to the increment() function:

• How to decrease a value using FieldValue in Firestore (SWIFT)?