Uniqueness Validator

[Uzzal Devkota]

Hey guys,

I added a uniqueness validator as following:

public class UniquenessValidator extends ValidatorAdapter {

    private final String attribute;

    public UniquenessValidator(String attribute) {

        this.attribute = attribute;

        setMessage("should be unique");

    }

    @Override

    public void validate(Model m) {

        if(!Model.where(attribute + " = ?", m.get(attribute)).isEmpty()) {

            m.addValidator(this, attribute);

        }

    }

}

// field: username

public class User extends Model {

    static {

        validateWith(new UniquenessValidator("username"));

    }

}

It works!. But, I was wondering if it is the optimal way to validate uniqueness. Especially the following line:

if(!Model.where(attribute + " = ?", m.get(attribute)).isEmpty())

Thanks.

[Uzzal Devkota]

Sorry, didn't check for update method. Doesn't validate while updating.

The validate method should be like following (Now works in all cases):

    @Override

    public void validate(Model m) {

        if (!Model.where(attribute + " = ? AND id IS NOT ?", m.get(attribute), m.getId()).isEmpty()) {

            m.addValidator(this, attribute);

        }

    }

m.getId() returns null for new record.

Still, the question remains. Is the query optimal?

Model.where(attribute + " = ? AND id IS NOT ?", m.get(attribute), m.getId()).isEmpty()

Thanks.

[Igor Polevoy]

No, it is not optimal, because: 

1. It will potentially load many model instances while you only need one attribute. 

2. It is not thread safe - while you are checking, another DB connection might update the values. 

Base.count(): 

http://ipsolutionsdev.com/activejdbc/org/javalite/activejdbc/Base.html#count(java.lang.String, java.lang.String, java.lang.Object...)

You can do this: 

If(Base.count("your_table", "query to filter", ... optional params) > 0){

// not empty

}else{

//empty

}

tx

[Uzzal Devkota]

And how would I get the table name from an instance of "Model" ? Could not find in the docs. :(

[Uzzal Devkota]

Oh there is this method that returns the table name of the model:

Model.getTableName();

So my method would look like:

    @Override

    public void validate(Model m) {

        if(Base.count(Model.getTableName(), attribute + " = ? AND id IS NOT ?", m.get(attribute), m.getId()) > 0) {

            m.addValidator(this, attribute);

        }

    }

I guess it is final.

Thanks Igor. Hope to get help in future as well.

[Uzzal Devkota]

Still confused how "Model.getTableName()" returns the table name. o.O

[Igor Polevoy]

This should work: 

this.getMetaModelLocal().getTableName();

[Uzzal Devkota]

I'm using activejdbc version 1.4.8. And there is getMetaModel() class method instead of getMetaModelLocal() instance method.

What's the point in calling: this.getMetaModelLocal().getTableName();

when you can get the table name by: Model.getTableName();

Any differences between these two approach?

Ayways thanks igor for reply. :)

[Igor Polevoy]

Because Model.getTableName() operates on class Model, not your model. Chances are it will not provide you with a table name 

[Uzzal Devkota]

Yes, that was my concern.

But, there is no "this.getMetaModelLocale()" method in activejdbc 1.4.8 :(

[Igor Polevoy]

sorry, typo: getMetaModelLocal()

[Uzzal Devkota]

Thanks.

[Se]

would this be correct then?

@Override

    public void validate(Model m) {

        if(Base.count(this.getMetaModelLocal().getTableName(), attribute + " = ? AND id IS NOT ?", m.get(attribute), m.getId()) > 0) {

            m.addValidator(this, attribute);

        }

    }

The if-statement doesn't compile though:

error: cannot find symbol

        if(Base.count(this.getMetaModelLocal().getTableName(), attribute + " = ? AND id IS NOT ?", m.get(attribute), m.getId()) > 0) {

  symbol: method getMetaModelLocal()

[Igor Polevoy]

Ag, sorry about that. This will work:

String tableName = Registry.instance().getTableName(m.getClass())

where "m" is an instance of your model 

tx

[Se]

Still doesn't compile throwing 'error: getTableName(Class<? extends Model>) has protected access in Registry'

This is the method itself, for the reference:

   public void validate(Model m) {

if(Base.count(Registry.instance().getTableName(m.getClass()), attribute + " = ? AND id IS NOT ?", m.get(attribute), m.getId()) > 0) {

[Igor Polevoy]

sorry about that, was trying in the  same project/package, did not see that.

This will do:

System.out.println(Registry.instance().getMetaModel(m.getClass()).getTableName());

tx

[Se]

This works. Thanks a lot Igor! Although I had to correct the query for the mysql.

For those who would stumble here later, the final validator class is as follows (though you may need to modify the query for your DBMS):

public class UniquenessValidator extends ValidatorAdapter {

private final String attribute;

public UniquenessValidator(String attribute) {

this.attribute = attribute;

setMessage("should be unique");

}

@Override

public void validate(Model m) {

if(Base.count(Registry.instance().getMetaModel(m.getClass()).getTableName(), attribute + " = ? AND id != ?", m.get(attribute), m.getId()) > 0) {

m.addValidator(this, attribute);

}

}

}

[Igor Polevoy]

I wonder if we might create a separate module for third party contributions like this? 

I do not feel including it because of a potential race condition, but at the same time some people might find it useful 

thoughts?

[Igor Polevoy]

I meant to say: "I do not feel including it into the framework proper..."

[Seva]

I think featuring it on the Validators page on the website would be great. Not sure about a separate module, but dropping it into the examples folder as part of the custom validator examples could be useful.
As for the race condition, how does Rails ActiveRecord solve this? I think the uniqueness validator definitely must be part of the framework.

Also, it would be great to open source the website so fixes, improvements and better examples could be contributed.

[Igor Polevoy]

Seva, maybe you are right, and it should be part of framework. Will integrate iater on.

We are working on the site, but things are slower than they should be. The documentation pages are being converted to Markdown files hosted on Github, so everyone can be contribute (in about 2 weeks time)

As far as how Rails does it, not sure, but worth looking. 

thanks

[Igor Polevoy]

filed this: https://github.com/javalite/activejdbc/issues/234

Would you like to send in a PL for this?

tx