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));
    }

If you set the variables to null, Contains() would throw an exception. — svick
– svick, Commented Oct 10, 2011 at 10:26
@svick of course but i would check this in my statement. Just want an idea of how others handle this. — Richard Banks
– Richard Banks, Commented Oct 10, 2011 at 10:28

Hans Keﬆing · Accepted Answer · 2011-10-10 10:30:59Z

8

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".

answered Oct 10, 2011 at 10:30

Hans Keﬆing

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Comments

Joey · Accepted Answer · 2011-10-10 10:43:00Z

How about something like this:

if (!string.IsNullOrWhiteSpace(jobNumber)) return _context.Jobs.Where(j => j.JobNumber.Contains(jobNumber));
if (!string.IsNullOrWhiteSpace(jobName)) return _context.Jobs.Where(j => j.JobName.Contains(jobName));
if (!string.IsNullOrWhiteSpace(projectDirectorName)) return _context.Jobs.Where(j => j.ProjectDirectorFullName.Contains(projectDirectorName));
if (!string.IsNullOrWhiteSpace(groupName)) return _context.Jobs.Where(j => j.GroupName.Contains(groupName));
else throw new ArgumentException ("No arguments specified");

Or something that reads better:

if (!string.IsNullOrWhiteSpace(jobNumber)) return FilterJobsByNumber(jobNumber);
if (!string.IsNullOrWhiteSpace(jobName)) return FilterJobsByName(jobName);
if (!string.IsNullOrWhiteSpace(projectDirectorName)) return FilterJobsByDirector(projectDirectorName);
if (!string.IsNullOrWhiteSpace(groupName)) return FilterJobsByGroupName(groupName);
else throw new ArgumentException ("No arguments specified");

For suitably defined FilterJobsByNumber etc.

DimonZa · Accepted Answer · 2011-10-10 10:46:37Z

0

Maybe it can helps.

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

answered Oct 10, 2011 at 10:46

DimonZa

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Comments

Peter Mortensen · Accepted Answer · 2014-04-04 16:59:03Z

0

You can try to use

string.IsNullOrWhiteSpace(yourString);  // .NET 4.0

OR

string.IsNullOrEmpty(yourString);

And if it is true, return an empty collection.

edited Apr 4, 2014 at 16:59

Peter Mortensen

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answered Oct 10, 2011 at 10:27

Stecya

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Comments

bala Selvanayagam · Accepted Answer · 2011-10-10 11:24:56Z

-1

It should be

String.IsNullOrWhitespace and Trim()

see my code

 NorthwindDataContext db= new NorthwindDataContext();
               db.Log = sw;
               var oList = db.Categories
                   .Where(j =>
                            ( string.IsNullOrWhiteSpace(txtName.Text) || j.CategoryName.StartsWith(txtName.Text.Trim()))
                            &&
                            (string.IsNullOrWhiteSpace(txtDescription.Text) || j.Description.StartsWith(txtDescription.Text.Trim()))   
                          )
                   .Select(p => new { Name = p.CategoryName ,Description =p.Description }).ToList();

answered Oct 10, 2011 at 11:24

bala Selvanayagam

1

Comments

Felix C · Accepted Answer · 2011-10-10 10:28:30Z

-2

I think String.IsNullOrWhitespace check is the best.

answered Oct 10, 2011 at 10:28

Felix C

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1 Comment

Felix C Over a year ago

No idea what you are talking about, but I did not down vote your answer.. My answer is really old and does not match to the topic.. I think they changed the question afterwards, otherwise I would not had suggested this answer. But I never down voted other answers in this topic.

Tauseef · Accepted Answer · 2015-05-11 19:45:09Z

Assuming that you have applied .Trim() on your search terms before getting into your this code block, modify the code as follows:

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

The point here is that you don't need to add the if conditions on your search terms. You may have multiple fields for search and it would just work fine.

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