Transform.from does nothing when column is NULL

[rrgoncalves]

Issue type:

[ ] question
[x] bug report
[ ] feature request
[ ] documentation issue

Database system/driver:

[ ] cordova
[ ] mongodb
[x] mssql
[x] mysql / mariadb
[x] oracle
[x] postgres
[ ] sqlite
[ ] sqljs
[ ] react-native
[ ] expo

TypeORM version:

[ ] latest
[ ] @next
[x] 0.2.11 (or put your version here)

Steps to reproduce or a small repository showing the problem:

Have a NULL value in a column like user.name and try to transform it with the following code:

// user.ts

@Entity("usuario", { schema: "myschema" })
export class user { 
      @Column({
        name: "name",
        type: 'text',
        transformer: {
          to(n) { 
            return n === undefined ? null : n 
          },
          from(n) { 
            return n === null ? undefined : n
          },
        }
    })
}

So, I was checking the code from PostgresDriver.js (/driver/postgres/PostgresDriver.js) and found out that there's no check if there's a transformer function set in the @Column decorator, and the code always checks first if the value if either null or undefined and returns it. As shown below:

PostgresDriver.prototype.prepareHydratedValue = function (value, columnMetadata) {
        if (columnMetadata.type === Boolean) {
            value = value ? true : false;

        // [...]
}

The fix should be something as simple as checking if the transformer exists and if it does, execute it:

PostgresDriver.prototype.prepareHydratedValue = function (value, columnMetadata) {
        if (columnMetadata.transformer) 
           return columnMetadata.transformer.from(value);

        if (columnMetadata.type === Boolean) {
            value = value ? true : false;

        // [...]
}

Some other people (##2777) and I believe the transformer should be executed nonetheless.

I'm willing to send a PR and add tests to fix such issue.

PS: MongoDriver got it right:

MongoDriver.prototype.prepareHydratedValue = function (value, columnMetadata) {
  if (columnMetadata.transformer)
    value = columnMetadata.transformer.from(value);
  return value;
};

Thanks!

[sroze]

Definitely, agree. Got this issue as of now :/