Check if an SOQL query is valid without actually executing it

Question

I'm building a system where a user will be providing me with a query through a UI. This query will then be used in an Async Apex Job, by passing it as a param to Database.getQueryLocator in the start method.

Initially, I was using Database.query or Database.countQuery for validating a query and catching possible exceptions. But in actuality, there could be millions of records in which case these functions will throw an error saying I've exceeded governor limits.

Does Salesforce provide a way of compiling a query just to check whether it is valid? A quick Google search turns up nothing.

Answer 1

You might be able to accomplish this by executing the query given with an additional LIMIT 0 at the end. You'll still use one SOQL query, but I don't believe this will count against the total number of rows retrieved. Something like:

string userQuery = 'select ID from Contact where Name like \'myContact%\'';
try
{
    Database.Query(userQuery + ' LIMIT 0');
}
catch(QueryException ex)
{
    //Error handling
}

This will not work for aggregate queries that do not have a group by function, but I believe limit always comes at the end of queries, so it ought to work with any others that don't already set a limit. If your user queries can/will have limit set, you could add some parsing to check if the limit is there, and if so validate it and then run the query with it set to 0.