Jira custom script validator: check if input textbox exists - textbox

Question

I am totally new to Jira. In fact I don't even know where to start. I went to the jira atlassian website but got nothing solid enough to help me. I would like to validate if the information entered into a textbox already exists. I clicked around jira and ended up on the screen below:
Now I would like to find out the following:
Which programming language should be used for validation ? Is it Java
If the name of the custom field(of type Textbox) is XYZ and I wanna if check if value entered into XYZ already exist, how do I go about doing that ? Can I just write conditional statements in Java ?
I wrote some stuff and nothing worked.

Answer 1

That's a screenshot from the Script Runner add-on.
There are some documentation and examples for custom validators here.
You can also find an example here that shows how to query the JIRA (or an external) database from a groovy script. Ie.:
import com.atlassian.jira.component.ComponentAccessor
import groovy.sql.Sql
import org.ofbiz.core.entity.ConnectionFactory
import org.ofbiz.core.entity.DelegatorInterface
import java.sql.Connection
def delegator = (DelegatorInterface) ComponentAccessor.getComponent(DelegatorInterface)
String helperName = delegator.getGroupHelperName("default");
def sqlStmt = """
SELECT project.pname, COUNT(*) AS kount
FROM project
INNER JOIN jiraissue ON project.ID = jiraissue.PROJECT
GROUP BY project.pname
ORDER BY kount DESC
"""
Connection conn = ConnectionFactory.getConnection(helperName);
Sql sql = new Sql(conn)
try {
StringBuffer sb = new StringBuffer()
sql.eachRow(sqlStmt) {
sb << "${it.pname}\t${it.kount}\n"
}
log.debug sb.toString()
}
finally {
sql.close()
}
For anything that gets a bit complex it's easier to implement your script in a groovy file and make it available to Script Runner via the file system. That also allows you use a vcs like git to easily push/pull your changes. More info about how to go about that, is here.