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The Reel

Representing state flow through file sequences

A Reel ties together Frames into a linear state flow model. The successful execution of all Frames belonging to a Reel signifies the end of a complete object state transition.

Reel - the sum of all Frames in a directory that share the same Reel name:

  • Represents a linear state flow diagram.

Final Frame - the last Success Frame of a Reel sequence:

  • Contains a return body holding the final desired state of a particular object.
  • A Reel's intent is tied to the existence of a Final Frame, in other words, the return body of the final Frame is the keystone of any Reel sequence.

The directory shown below holds the Frames needed to create a fully populated "User" object starting with user creation and ending with a query that returns the expected "User":

user_reel
├── usr.01e.createuser.fr.json
├── usr.01s.createuser.fr.json
├── usr.01se.createuser.fr.json
├── usr.02s.changeaddress.fr.json
├── usr.03s.changebirthdate.fr.json
├── usr.04s.changebirthlocation.fr.json
├── usr.06e.changeemail.fr.json
├── usr.06s.changeemail.fr.json
├── usr.07s.confirmemail.fr.json
├── usr.08s.changename.fr.json
└── usr.09s.getuser.fr.json

Listing 1: An example Reel in the user_reel directory. The Reel sequence indicates the steps taken to eventually return a representation of a "User" object in the final state.

Reel nomenclature

┌─────────── Reel name              // usr
│   ┌─────── Sequence number        // 01
│   │ ┌───── Frame type             // se
│   │ │  ┌── Command name           // createuser
▼   ▼ ▼  ▼
usr.01se.createuser.fr.json
                    ▲
                    └─ Frame suffix // .fr.json

Listing 2: A breakdown of a Frame's filename.

Sequence number - a number representing a particular step in an object's state transition:

  • The presence of a Frame does not necessarily allude to a state transition. Most Error Frames, for example, do not modify state.
  • A sequence number must be a whole number unless there are multiple Frame types associated with a particular sequence number, then the sequence number must be suffixed with a decimal value delimited by an underscore:

user_reel
├── usr.01e_1.createuser.fr.json // no first name
├── usr.01e_2.createuser.fr.json // no email
└── usr.01s.createuser.fr.json   // user created successfully

Listing 3: A sequence number with more than one Error Frame.

  • Whole sequence number - the integer representation of a sequence number indicating an object state.

Frame type - defined by the return body of a Frame:

  1. Error Frame - Frame with a return body holding an error status code.
    • represented by the letter e.
    • precedes a Success Frame sharing the same whole sequence number.
  2. Success Frame - Frame with a return body holding a success status code:
    • represented by the letter s.
    • Typically indicates a state transition.
    • A sequence number should aim to be referenced by only one success Frame.
  3. Post Success Error Frame aka P.S. Error Frame - an Error Frame that must be preceded by a Success Frame sharing the same whole sequence number:
    • represented by the letters se.

  $ jq '.response.body' user_reel/01se.usr.createuser.fr.json
  "error: unable to create user, entry already exists"

Listing 4: An example error message for a post success Error Frame.

Reel name - indicates the Reel that a Frame belongs to:

  • A Frame must belong to only one Reel.

Reel prefix - the concatenation of a Frame's sequence number, Frame type, and Reel name:

usr.01se.createuser.fr.json
└──────┤
       └─ Reel prefix // usr.01se

Listing 5: Delineation of a Frame file's Reel prefix.

  • Fully represents a Frame's relative placement in a Reel sequence.

Method name - represents the particular RPC command or REST endpoint coinciding with a Frame's request method.

Type suffix - a filename ending in .fr.json indicates said file is a filmReel template Frame.

filmReel concepts: