Import LB3 model JSON file to LB4 model class

[bajtos]

As an LB3 user migrating my model definition files to LB4, I would like to call lb4 CLI to generate an LB4 model class from my LB3 model JSON file.

lb4 import-lb3-models legacy-lb3app/server/server.js
# load the LB3 app
# ask the user which models to import
# create src/models/product.ts etc.

The initial version should handle property definitions only.

For example, let's take an LB3 Product model with a name property:

{
  "name": "Product",
  "base": "PersistedModel",
  "properties": {
    "name": {
      "type": "string",
      "required": true
    }
  }
}

This LB3 definition should be translated into an LB4 TypeScript model class:

@model()
class Product extends Entity {
  @property({required: true})
  name: string;
}

Acceptance criteria

• A new CLI flag for lb4 model, or perhaps a new command, accepting a path to LB3 model file, that will scaffold (code-generate) an LB4 model file from LB3 definition. See Model Discovery #2245 for related prior work. (/cc @marvinirwin)
  --> see CLI: Import LB3 model(s) into LB4 project [EXPERIMENTAL] #3688
• The following base model classes should be recognized and mapped to LB4:
  • Model -> Model
  • PersistedModel -> Entity
  • KeyValueModel -> (to be determined)
    When the base model class is not recognized, the CLI should abort with a descriptive error.
    --> see CLI: Import LB3 model(s) into LB4 project [EXPERIMENTAL] #3688
• The following model settings should trigger a warning when a non-empty value is provided in LB3 model file:
  • relations
  • method
  • mixins
  • acls
    --> see CLI: Import LB3 model(s) into LB4 project [EXPERIMENTAL] #3688
• All other model settings should be copied as-is to LB4 model definition. IMPORTANT: settings can be specified either at top-level or inside options property, we need to support both flavors. Notable settings to test & support:
  • forceId
  • strict
  • connector-specific config like SQL table name and MongoDB collection name
    --> see CLI: Import LB3 model(s) into LB4 project [EXPERIMENTAL] #3688
• Documentation at CLI level
  --> see CLI: Import LB3 model(s) into LB4 project [EXPERIMENTAL] #3688
• A blog post
• Follow-up stories for things that were left out of the initial implementation. Most notably support for non-default base model classes and relations.

See #2036 for the next step that will allow developers to take LB4 model and expose it via REST with little to no configuration.

Open discussion points & todos

• Should we offer built-in models like User and AccessToken for importing?
• Should we select all models by default?
• How to automate model selection? Should we introduce a cli option like --models User,AccessToken? Use positional arguments like lb4 import-model my-lb3-app User AccessToken?
• Process TODO & FIXME comments in the initial implementation CLI: Import LB3 model(s) into LB4 project [EXPERIMENTAL] #3688 and convert them to sub-tasks or follow-up issues
• Write automated test to verify import of models attached to the following connectors:
  • SQL (MySQL or Postgres)
  • MongoDB (how is ObjectID type handled?)
  • Cloudant (how is _rev property handled?)

Out of scope

• relations
• remote methods
• ACLs
• mixins
• Custom model property settings must be preserved, e.g. SQL column names.
• A new section in the migration guide

[marioestradarosa]

@bajtos , currently the lb4 @model decorator can take the lb3 version model in json format as follows:

@model(
{
  "name": "Product",
  "properties": {
    "name": {
      "type": "string",
      "required": true
    }
  }
})
class Product extends Entity {
}

[emonddr]

How are we going to handle the model-config.json ?

[buokae]

Is there a migration manual somewhere? I have eight months left to migrate my project from lb3 to lb4 and no idea where to start.