LINQ multiple where statement mvc - asp.net-mvc

Question

This code works only if I complete the 3 fields:
website, author, and content.
I want to complete 1 field, 2 fields or 3 fields (non completed fields are null) and search according to that
var posts = from p in db.Posts
where ((p.PostDate >= fd && p.PostDate <= td)
&& p.WebSite.Equals(WebSite)
&& p.PostAuthor.Contains(Author)
&& p.PostText.Contains(Content)
|| WebSite == null || Author == null || Content == null)
select p;
I tried this code but don't working too:
var posts = from p in db.Posts
select p;
if (WebSite != null)
{
posts = from p in db.Posts
where p.WebSite.Equals(WebSite)
select p;
}
if (Author != null)
{
posts = from p in db.Posts
where p.PostAuthor.Contains(Author)
select p;
}
if (Content != null)
{
posts = from p in db.Posts
where p.PostText.Contains(Content)
//Count and date is missing
select p;
}
return View("Index", posts);
I need like this for 1 parameter but for 3:
var posts = from p in db.Posts
where p.PostTitle.Contains(searchTerm) || searchTerm==null
select p;
return View(posts);

Answer 1

First you need to prepare non filtered IQueryable object without selecting the output:
IQueryable<Post> query = from p in posts;
Then apply filter according to your filter conditions
if (webSite != null)
{
posts = posts.Where(p => p.WebSite.Contains(webSite));
}
if (author != null)
{
posts = posts.Where(p => p.PostAuthor.Contains(author));
}
Finnaly run query
var result = posts.ToArray();
Another approach is to create fulltext index on the table and search by fulltext in indexed columns. It has better results then searching in the three fields separately.

Answer 2

Change your code to this:
var posts = from p in db.Posts
select p;
if (!string.IsNullOrEmpty(WebSite))
{
posts = from p in posts
where p.WebSite.Equals(WebSite)
select p;
}
if (!string.IsNullOrEmpty(Author))
{
posts = from p in posts
where p.PostAuthor.Contains(Author)
select p;
}
if (!string.IsNullOrEmpty(Content))
{
posts = from p in posts
where p.PostText.Contains(Content)
//Count and date is missing
select p;
}
return View("Index", posts.ToList());
An empty string is not the same as a null string.
Edit: you should probably execute the query before sending it to the view.
Using LINQ to Entities:
var posts = db.Posts.AsQueryable();
if (!string.IsNullOrEmpty(WebSite))
posts = posts.Where(p => p.WebSite.Equals(WebSite));
if (!string.IsNullOrEmpty(Author))
posts = posts.Where(p => p.PostAuthor.Contains(Author));
if (!string.IsNullOrEmpty(Content))
posts = posts.Where(p => p.PostText.Contains(Content));
return View("Index", posts.ToList());

Answer 3

Solution:
var posts = from p in db.Posts
where ((string.IsNullOrEmpty(WebSite) || p.WebSite.Equals(WebSite))
&& (string.IsNullOrEmpty(Author) || p.PostAuthor.Contains(Author))
&& (string.IsNullOrEmpty(Content) || p.PostText.Contains(Content))
)
select p;

Answer 4

Try the following:
var posts = from p in db.Posts
where ((p.PostDate >= fd && p.PostDate <= td)
&& ((string.IsNullOrEmpty(WebSite) || p.WebSite.Equals(WebSite))
|| (string.IsNullOrEmpty(Author) || p.PostAuthor.Contains(Author))
|| (string.IsNullOrEmpty(Content) || p.PostText.Contains(Content)))
)
select p;

Answer 5

Just replace db.Posts with posts in the three conditional searches, so for the first one:
if (WebSite != null)
{
posts = from p in posts
where p.WebSite.Equals(WebSite)
select p;
}