CODEWITHSUNDEEP
c#asp.net-mvclinqasp.net-corelambda
Aram
Aram

Reputation: 63

How Can I Building The Lambda Expressions Dynamically With String

This is my code. 

[HttpPost]
public ActionResult TopProjects(FormCollection form)
{
  bool top, desgin, implement;
  string str = "";
  if (string.IsNullOrEmpty(form["top"])) { top = false; } else { top = true;str += "x=>x.IsTopProject==top"; }
  if (string.IsNullOrEmpty(form["desgin"])) { desgin = false; } else { desgin = true; str += "&& x.IsAnDesigning==desgin"; }
  if (string.IsNullOrEmpty(form["implement"])) { implement = false; } else { implement = true;str += "&& x.IsAnImplementation==implement"; }

   return View(blProject.Select().Where(str));
 }

The lambda get error from str. How can i solving it?

Upvotes: 0

Views: 50

Answers (1)

Harald Coppoolse
Harald Coppoolse

Reputation: 30464

Apparently blProject an object of a class that implements IQueryable of some class, let's say it implements IQueryable<BlProjectItem>:

IQueryable<BlProjectItem> blProjects = ...

Apparently every BlProjectItem has at least three boolean properties:

class BlProjectItem
{
    public bool IsTopProject {get; set;}
    public bool IsAnDesigning {get; set;}
    public bool IsAnImplementation {get; set;}

    ...
}

You define three Booleans in a difficult way, you meant to say:

bool top =       String.IsNullOrEmpty(form["top"]));
bool design =    String.IsNullOrEmpty(form["desgin"]);
bool implement = String.IsNullOrEmpty(form["implement"]);

Depending on whether on the values of top / design / implement this is what you want

 Top   Design   Implement     All BlProjectItems where
  0      0         0          !IsTopProject && !IsAnDesigning && !IsAnImplementation
  0      0         1          !IsTopProject && !IsAnDesigning &&  IsAnImplementation
  0      1         0          !IsTopProject &&  IsAnDesigning && !IsAnImplementation
  0      1         1          !IsTopProject &&  IsAnDesigning &&  IsAnImplementation

  1      0         0           IsTopProject && !IsAnDesigning && !IsAnImplementation
  1      0         1           IsTopProject && !IsAnDesigning &&  IsAnImplementation
  1      1         0           IsTopProject &&  IsAnDesigning && !IsAnImplementation
  0      1         1           IsTopProject &&  IsAnDesigning &&  IsAnImplementation

In other words you want:

 .Where(item => item.IsTopProject == top
             && item.IsAnDesigning == design
             && item.IsAnImplementation == implement)

Your function will be like:

public ActionResult TopProjects(FormCollection form)
{
    bool top =       String.IsNullOrEmpty(form["top"]));
    bool design =    String.IsNullOrEmpty(form["desgin"]);
    bool implement = String.IsNullOrEmpty(form["implement"]);

    var query = blProject.Where(item => item.IsTopProject == top
             && item.IsAnDesigning == design
             && item.IsAnImplementation == implement)

    // only if you don't want all properties of BlProjectItem:
    .Select(item => new
    {
         // Select the items that you want, e.g.
         Id = item.Id,
         Name = item.Name,
         ...
    });

    return view(Query);
}

Upvotes: 1

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