PROBLEM:
I want to create a linq query of an in memory object based on 3 possible
filters, and the only way I can think is something like the code below.
Besides being verbose, I'm repeating myself. How can I rewrite this??

Thanks for your help - BH

CODE:
I've included the whole class for context, but it's the OnCriteriaChanged
method at the bottom that's getting out of hand (and I haven't finished all
combinations!)

public class ProjectPickerPresenter
{
private readonly List<WddProject> _allProjects;
public List<string> PrefixList { get; private set; }
public string PrefixFilter { get; set; }
public string SequenceNumberFilter { get; set; }
public string DescriptionFilter { get; set; }
public List<WddProject> DisplayProjects { get; private set; }

public ProjectPickerPresenter() {
_allProjects = new
OpenProjects(Connection.DbConnection(Connection.Env.Dev_IdentityDriven));
DisplayProjects = _allProjects;
PrefixList = new List<string>((from project in _allProjects orderby
project.Prefix select project.Prefix).Distinct());
}

public void OnCriteriaChange() {
// no filters
if( (PrefixFilter==null) && (SequenceNumberFilter==null) &&
(DescriptionFilter==null)) {
DisplayProjects = _allProjects;
}
// one filter only
else if ((PrefixFilter != null) && (SequenceNumberFilter == null) &&
(DescriptionFilter == null)) {
var result = _allProjects.Where(project =>
project.Prefix.Equals(PrefixFilter));
if (result != null) DisplayProjects = new
List<WddProject>(result);
}
else if ((PrefixFilter == null) && (SequenceNumberFilter != null) &&
(DescriptionFilter == null)) {
var result = _allProjects.Where(project =>
project.SequenceNumber.StartsWith(SequenceNumberFilter));
if (result != null) DisplayProjects = new
List<WddProject>(result);
}
else if ((PrefixFilter == null) && (SequenceNumberFilter == null) &&
(DescriptionFilter != null)) {
var result = _allProjects.Where(project =>
project.Description.Contains(DescriptionFilter));
if (result != null) DisplayProjects = new
List<WddProject>(result);
}
// two filters together
else if ((PrefixFilter != null) && (SequenceNumberFilter == null) &&
(DescriptionFilter != null)) {
var result = _allProjects.Where(project =>
project.Prefix.Equals(PrefixFilter) &&
project.Description.Contains(DescriptionFilter));
if (result != null) DisplayProjects = new
List<WddProject>(result);
}
}
}

Berryl Hesh wrote:
> PROBLEM:
> I want to create a linq query of an in memory object based on 3 possible
> filters, and the only way I can think is something like the code below.
> Besides being verbose, I'm repeating myself. How can I rewrite this??
>
> Thanks for your help - BH
>
> CODE:
> I've included the whole class for context, but it's the OnCriteriaChanged
> method at the bottom that's getting out of hand (and I haven't finished all
> combinations!)
>
>
> public void OnCriteriaChange() {
> // no filters
> if( (PrefixFilter==null) && (SequenceNumberFilter==null) &&
> (DescriptionFilter==null)) {
> DisplayProjects = _allProjects;
> }
> // one filter only
> else if ((PrefixFilter != null) && (SequenceNumberFilter == null) &&
> (DescriptionFilter == null)) {
> var result = _allProjects.Where(project =>
> project.Prefix.Equals(PrefixFilter));
> if (result != null) DisplayProjects = new
> List<WddProject>(result);
> }
> else if ((PrefixFilter == null) && (SequenceNumberFilter != null) &&
> (DescriptionFilter == null)) {
> var result = _allProjects.Where(project =>
> project.SequenceNumber.StartsWith(SequenceNumberFilter));
> if (result != null) DisplayProjects = new
> List<WddProject>(result);
> }
> else if ((PrefixFilter == null) && (SequenceNumberFilter == null) &&
> (DescriptionFilter != null)) {
> var result = _allProjects.Where(project =>
> project.Description.Contains(DescriptionFilter));
> if (result != null) DisplayProjects = new
> List<WddProject>(result);
> }
> // two filters together
> else if ((PrefixFilter != null) && (SequenceNumberFilter == null) &&
> (DescriptionFilter != null)) {
> var result = _allProjects.Where(project =>
> project.Prefix.Equals(PrefixFilter) &&
> project.Description.Contains(DescriptionFilter));
> if (result != null) DisplayProjects = new
> List<WddProject>(result);
> }
> }
> }
>

How about writing a comparer method? Something like:

private bool Compare(WddProject project) {
return
(PrefixFilter == null || project.Prefix == PrefixFilter) &&
(SequenceNumberFilter == null ||
project.SequenceNumber.StartsWith(SequenceNumberFilter)) &&
(DescriptionFilter == null ||
project.Description.Contains(DescriptionFilter));
}

public void OnCriteriaChange() {
if( (PrefixFilter==null) && (SequenceNumberFilter==null) &&
(DescriptionFilter==null)) {
DisplayProjects = _allProjects;
} else {
var result = _allProjects.Where(Compare);
if (result != null) DisplayProjects = result.ToList();
}
}

--
Göran Andersson
_____
http://www.guffa.com