Transforms

Transforms

Transformers allow you to overwrite the value returned from the database before validating it. They work in a similar way to validators, except that transformers actually overwrite the value.

Let's go back to the example with the same LogsDTO

class LogsDTO implements Validate {
    
    @Result()
    @IsNumber()
    public id!: number;
    
    @Result('date')
    @IsDate()
    public logDate!: Date;
    
    @Result('user')
    @IsSafeString()
    @Min(3)
    @Max(32)
    public nickname!: string;
    
    public validateErrors: Set<string> = new Set();
}

Let's say you're using @kop3yka/Time library and want a regular Date to be transformed into a Time class object. You can use transformers for this

First, let's create the transformer itself.

const ToTime = () => TransformFactory.createTransform(
    (value: any) => { 
        return new Time(value);
    }
)

Now we can use it for our DTO

class LogsDTO implements Validate {
    
    @Result()
    @IsNumber()
    public id!: number;
    
    @Result('date')
    @ToTime()
    public logDate!: Time;
    
    @Result('user')
    @IsSafeString()
    @Min(3)
    @Max(32)
    public nickname!: string;
    
    public validateErrors: Set<string> = new Set();
}

There are also built-in transformers. For example, ToString, ToNumber, ToDate

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