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Auto increment

MongoDB has no auto increment column. API Maker gives one to every database : mark a number field with isAutoIncrementByAM, and every row saved through the schema APIs gets the next number.

In short

  • order_no: { __type: EType.number, isAutoIncrementByAM: { start: 1000, step: 5 } }
  • One counter per field, in the Redis of API Maker, shared by every server : no two rows get the same number.
  • See and change the counters on Database → Auto Increments.
Schema order_no: { __type: EType.number, isAutoIncrementByAM: { start: 1000, step: 5 } } ; true means start 1, step 1.
Counter One per field, kept in the internal Redis of API Maker, shared by every server.
Page Database → Auto Increments : every counter of the account, with its last value, which you can edit.
Git The counters of a branch are written to Auto Increments/auto_increments_<branch>.yml in the repository.

How the next value is chosen

  1. The counter of the field is increased by step. This is atomic : two servers saving at the same time get two different numbers.
  2. When the result is not above start (a new counter, or a counter reset below start), API Maker reads the highest value the table already has : the next value is that maximum plus step, and at least start.
  3. The value is written in the row. A value sent in the payload is replaced.
Start Step Counter Highest in table Next value
1000 5 1020 1025
1000 5 none 1100 1105
1000 5 none empty table 1000
1 1 none empty table 1
  • Rows inserted outside API Maker are picked up the next time the counter starts from scratch ; edit the counter on the Auto Increments page to realign it right away.
  • isAutoGenerateByAM on the same field wins, and isAutoIncrementByDB disables it : let the database count when it can.
  • Like a database sequence, the numbers can have gaps : a save refused after its number was counted (a value of another field that is not valid, for example) keeps that number.

The Auto Increments page

  • Lists the counters of the environment : instance, database, table, field path and the last generated value.
  • Edit sets the last value ; the next row gets it plus step. The dialog shows the values the next number will be the maximum of.
  • Delete removes a counter : the next save reads the highest value of the table again.

With Git

  • A pull writes the counters of the branch into Redis when they are missing there ; a counter which exists on the server is never replaced by the one of Git.
  • A new environment therefore starts from the counters of the branch, and a running one keeps its own.