handling empty strings using linq

Question

I have a linq statement that searches a number of fields based on user input from a form. Only 1 form field is required, thus I need to handle empty string values. Whats the best way to handle this. Should i check the length of the string and then null the relevant vars and then check this in my linq statement or can i do something in my linq statement. My method is below :-

     public IEnumerable<Job> GetJobs(string jobNumber, string jobName, string projectDirectorName, string projectManagerName, string groupName) {
        return this._context.Jobs.Where(
            j => j.JobNumber.Contains(jobNumber) ||
                 j.JobName.Contains(jobName) ||
                 j.ProjectDirectorFullName.Contains(projectDirectorName) ||
                 j.GroupName.Contains(groupName));
    }

Answer 1

You could use this:

 public IEnumerable<Job> GetJobs(string jobNumber, string jobName, string projectDirectorName, string projectManagerName, string groupName) {
    IQueryable<Job> query = this._context.Jobs;

    if (!String.IsNullOrEmpty(jobNumber))
       query = query.Where(j => j.JobNumber.Contains(jobNumber));

    if (!String.IsNullOrEmpty(jobname))
       query = query.Where(j => j.JobName.Contains(jobName));

    // etc.

    return query;
}

If this will query the database, then that database will only get queried when you iterate over the results of this method, not for each ".Where".