Hi yadav2
Seblod comes with default capability to check via ajax whether something already exists. Have you tried that?
If so what do you need that is different?
Seblod default way:
In your content type form, select number 3 (Required / Validation + Stage)
Select "optional" from the Required / Validation Column. A Modal Window appears.
Select "Ajax - Availablility" from the Validation Select list.
New options appear in which you select the table and column that you want to validate against.
Underneath all of that is an input box labelled "field". I have never used it but I guess it is an alternative to the method described above in which you would enter the field you want to validate against.
Bucklash