Updating a Model

A model is updating using the DataContext.update method. It taks two parameters:

An EntityType, which is some Table-decorated class. (See the Models section.)
A model, which is an instance of the EntityType. The model must have at least the primary key set.

DataContext.update returns an UpdateModel instance, which is a type of Query. As such, you can use the toString method for debugging, and the execute method to run the query.

Update a Person Instance

Here’s how one could update the firstName of a Person record.

// Update the first name of the person with ID 1.
const person = new Person();

person.id = 1;
person.firstName = 'Marco';

const query: UpdateModel<Person> = dataContext
  .update(Person, person);

console.log(query.toString());

// If no rows are affected (i.e. if a person with an id of 1 does not
// exist), then an error will be raised.
await query.execute();

In this case, we’ve only updated one property, firstName; all other properties are ignored. It’s worth pointing out that Formn differentiates between undefined and null. In the above query, since person.lastName is undefined, Formn ignores it. If it were null, however, Formn would set the associated value to NULL in the database.

Also note the final comment. Updating a model is done by ID, and if the update does not affect any rows then an error will be raised. In the next section we’ll cover batch updates, which do not have this restriction.

Full Example

The example shown above is present in the formn-example repository under src/update/update-person.ts.

import {
  MySQLDataContext, ConnectionOptions, ConditionBuilder, UpdateModel
} from 'formn';

import { Person } from '../entity/person.entity';

async function main() {
  const connOpts: ConnectionOptions = require('../../connections.json');
  const dataContext = new MySQLDataContext();

  try {
    await dataContext.connect(connOpts);

    // Update the first name of the person with ID 1.
    const person = new Person();

    person.id = 1;
    person.firstName = 'Marco';

    const query: UpdateModel<Person> = dataContext
      .update(Person, person);

    console.log(query.toString());

    // If no rows are affected (i.e. if a person with an id of 1 does not
    // exist), then an error will be raised.
    await query.execute();
    await dataContext.end();
  }
  catch(err) {
    console.error(err);
  }
}

main();

It can be run with ts-node.

npx ts-node ./src/update/update-person.ts

Output will look like this.

UPDATE  `people` AS `people`
SET
`people`.`firstName` = :people_firstName_0
WHERE   (`people`.`personID` = :people_id_0)

Again, note that only the firstName is updated, and the update is by ID.