My action is :
[HttpPost]
public ViewResult SearchPost(FormCollection frm)
{
IList <post> p =db.posts.Include("user").ToList();
if (Request.Form["area"] != null)
{
if ((p!=null) && (p.Any()))
{
p =p.Where(a=>a.area==Request.Form["area"]).ToList();
}
}
if (Request.Form["floor"] != null)
{
if ((p!=null) && (p.Any()))
{
p = p.Where(a => a.floor ==
Request.Form["floor"]).ToList();
}
}
if (Request.Form["garage"] != null)
{
if ((p!=null) && (p.Any()))
{
p = p.Where(a => a.garage ==
Request.Form["garage"]).ToList();
}
}
return View(p);
}
it has shown no errors. but always return null. it should return filtered post objects or simply all posts without filtering. is there any problem ?? i can't find it .
I don't know the full signatures of the types that you are dealing with, but perhaps try this code and see if you get any better results:
[HttpPost]
public ViewResult SearchPost(FormCollection frm)
{
var area = Request.Form["area"];
var floor = Request.Form["floor"];
var garage = Request.Form["garage"];
return View(db.posts.Include("user")
.Where(a => area == null || a.area == area)
.Where(a => floor == null || a.floor == floor)
.Where(a => garage == null || a.garage == garage).ToList());
}
(This is essentially a rewrite of your code down into a single query that might help you with debugging.)
Related
I need to ignore null parameters in the where clause so that i can fetch the appropriate data with the applied filters from the user side. Inorder to acheive this, I am currently using the if..else nested approach which grows in size as the number of parameters grow. I would like to know if there is any other effecient way of handling this scenario by avoiding the number of lines and complexity and improving readablility
public List<Members> GetMembers(int currentPosition, string memberStatus,
string package, string packageStatus, string branch)
{
var members = new List<Members>();
if (package != null)
{
//include package
if (packageStatus != null)
{
//include package, packageStatus
if (branch != null)
{
//include package,packageStatus,branch
members = db.Members.Where(x => x.PackageName == package && x.PackageStatus == packageStatus && x.Branch == branch).ToList();
}
else
{
//include package,packageStatus
members = db.Members.Where(x => x.PackageName == package && x.PackageStatus == packageStatus).ToList();
}
}
else
{
if (branch != null)
{
//include package,branch
members = db.Members.Where(x => x.PackageName == package && x.Branch == branch).ToList();
}
else
{
//include package
members = db.Members.Where(x => x.PackageName == package).ToList();
}
}
}
else
{
if (packageStatus != null)
{
//include packageStatus
if (branch != null)
{
//include packageStatus,branch
members = db.Members.Where(x => x.PackageStatus == packageStatus && x.Branch == branch).ToList();
}
else
{
//include packageStatus
members = db.Members.Where(x => x.PackageStatus == packageStatus).ToList();
}
}
else
{
if (branch != null)
{
//include packageStatus,branch
members = db.Members.Where(x => x.PackageStatus == packageStatus && x.Branch == branch).ToList();
}
else
{
//include nothing
members = db.Members.ToList();
}
}
}
return members;
}
You can add those conditions to the query. It won't make for the most readable SQL, but assuming you find readable code more important and trust SQL Server's optimizer:
members = db.Members.Where(x =>
(package == null || x.PackageName == package) &&
(packageStatus == null || x.PackageStatus == packageStatus) &&
(branch == null || x.Branch == branch)
).ToList();
Alternatively, you could conditionally append Where()s to a variable of type IQueryable<Member>. See for example entity framework: conditional filter.
I would like to suggest a readable version of the method:
public List<Members> GetMembers(int currentPosition, string memberStatus,
string package, string packageStatus, string branch)
{
var members = new List<Members>();
members = db.Members.ToList();
if (package != null)
{
members = members.Where(x => x.PackageName == package);
}
if (packageStatus != null)
{
members = members.Where(x => x.PackageStatus == packageStatus);
}
if (branch != null)
{
members = members.Where(x => x.Branch == branch);
}
return members.ToList();
}
I think this works (haven't tried compiling it but it makes sense in my head)
public List<Members> GetMembers(int currentPosition, string memberStatus,
string package, string packageStatus, string branch)
{
List<Members> ret = db.Members()
if(memberStatus != null || package != null || packageStatus != null || branch != null)
{
ret = db.Members.Where(x =>
(memberStatus == null) ? (true) : (memberStatus == x.MemberStatus)
&& (package == null) ? (true) : (package == x.PackageName)
&& (packageStatus == null) ? (true) : (packageStatus == x.PackageStatus)
&& (branch == null) ? (true) : (branch == x.Branch)
).ToList();
}
return ret;
}
I have list of Countries and inside it have list of Places.
// ...
public IList<ICountriesDTO> Countries { get; set; }
public class CountriesDTO: ICountriesDTO
{
public IEnumerable<IPlacesDTO> Places { get; set;
}
I am trying to get list of Places that are not null.
allPlacesDTO.World.Countries
.SelectMany(x => x.Places == null ? null : x.Places)
.ToList();
But I receive a null exception when Places are null for their Countries object.
How can I do a null check for Places and just use return statement instead of doing select to null object, similar to what I have below?
if (allPlacesDTO.World.Countries.Places == null)
{
return;
}
Update:
My requirement was if there is no places in any of the countries just use the return statement to exit the current function without proceeding further. That was achieved by the accepted answer and Count function.
var lstAllPlaces = allPlacesDTO.World.Countries
.Where(x => x.Places != null)
.SelectMany(x => x.Places)
.ToList();
if (lstAllPlaces.Count() == 0)
{
return;
}
You can do the condition in where clause
allPlacesDTO.World.Countries.Where(x => x.Places != null)
.SelectMany(x => x.Places).ToList();
Or change the ternary operator to return new List() (it can be greedy)
I'm trying to accomplish an expression function alternative
private static Expression<Func<UserProfile, bool>> CompareFilter(FilterViewModel f)
{
...
}
on this one:
private static bool CompareFilter(UserProfile profile, FilterViewModel filter)
{
if (filter.FirstName != null)
{
if (profile.FirstName != null)
{
if (profile.FirstName.CompareTo(filter.FirstName) != 0)
{
return false;
}
}
else
{
return false;
}
}
if (filter.TownId != null)
{
if (profile.TownId != filter.TownId)
{
return false;
}
}
// true if at least one of the filter interests match
if (filter.InterestsIds != null)
{
var firstInterestFound = profile.Interests
.Where(i => filter.InterestsIds.Contains(i.Id))
.FirstOrDefault();
if (firstInterestFound == null)
{
return false;
}
}
...
return true;
}
Is there a way to fit this many nested if statements to a lambda expression or something else that will work for the expression function? The idea is the verification to go trough all the if statements and to return true only if all of them are not returning false.
Thanks in advance!
First of all, your current method is so long because you are not making good use of boolean logic. It can be simplified to this:
private static bool CompareFilter(UserProfile profile, FilterViewModel filter)
{
if (filter.FirstName != null && filter.FirstName != profile.FirstName)
{
return false;
}
if (filter.TownId != null && filter.TownId != profile.TownId)
{
return false;
}
// true if at least one of the filter interests match
if (filter.InterestsIds != null &&
!profile.Interests.Any(i => filter.InterestsIds.Contains(i.Id)))
{
return false;
}
...
return true;
}
You can turn this into a big hulking expression by inverting all the logic1:
private static bool CompareFilter(UserProfile profile, FilterViewModel filter)
{
return (filter.FirstName == null || filter.FirstName == profile.FirstName) &&
(filter.TownId == null || filter.TownId == profile.TownId) &&
(filter.InterestsIds == null ||
profile.Interests.Any(i => filter.Interests.Contains(i.Id)));
// etc. etc.
}
And once you have this, it's a piece of cake to turn it into a lambda and get your Expression<T>:
private static Expression<Func<UserProfile, bool>> CompareFilter(FilterViewModel f)
{
return profile =>
(filter.FirstName == null || filter.FirstName == profile.FirstName) &&
(filter.TownId == null || filter.TownId == profile.TownId) &&
(filter.InterestsIds == null ||
profile.Interests.Any(i => filter.Interests.Contains(i.Id)));
}
Technically, you can just || together all the conditions from the first method and put a big !( ) around it: return !( (...) || (...) || (...));, but inverting everything and joining the conditions with && is a lot nicer.
Looks like stupid question, but I just dont get it.
My entity:
public class Page
{
public int Id { get; set; }
//...
public int? ParentId { get; set; }
}
In controller:
db.Pages.First(x => x.ParentId == null);
Works as expected (returns some element).
But:
int? test = null;
db.Pages.First(x => x.ParentId == test);
Throws Sequence contains no elements
What do I miss?
I believe there's an oddity around nulls with some LINQ providers. Try:
var query = db.Pages.First(x => (test != null && x.ParentId == test) ||
(test == null && x.ParentId == null));
Alternatively, use different queries for the different situations:
var query = test == null ? db.Pages.First(x => x.ParentId == null)
: db.Pages.First(x => x.ParentId == test);
Basically this is because SQL treats NULL as unequal to itself, so:
WHERE X = Y
will still fail if both X and Y are null values. Using the == null part (with a literal null) forces a conversion to ISNULL or whatever the SQL equivalent is.
I agree it's a pain, and someone else may have a better workaround, but this may help you get going.
You could do something like this as a workaround:
int? test = null;
if(test.HasValue) {
db.Pages.First(x => x.ParentId == test.Value);
} else {
db.Pages.First(x => x.ParentId == null);
}
I'm assuming since int? is actually a Nullable<int> our linq-to-entities provider isn't comparing things right.
Try this (modified according to gdoron's comment. It now is exactly what gideon posted, so please accept his instead of mine):
int? test = null;
if(test.HasValue) {
db.Pages.First(x => x.ParentId == test.Value);
} else {
db.Pages.First(x => x.ParentId == null);
}
I have the following class:
public class DocumentCompare
{
public string Customer;
public string Filename;
public string Reference;
public DateTime? Date;
public override bool Equals(object obj)
{
if (obj == null)
return false;
DocumentCompare doc = obj as DocumentCompare;
if ((Object)doc == null)
return false;
return (doc.Customer == Customer) && (doc.Date == Date) && (doc.Filename == Filename) && (doc.Reference == Reference);
}
public bool Equals(DocumentCompare doc)
{
if ((object)doc == null)
return false;
return (doc.Customer == Customer) && (doc.Date == Date) && (doc.Filename == Filename) && (doc.Reference == Reference);
}
public override int GetHashCode()
{
return string.Format("{0}_{1}_{2}_{3}",Customer,Filename,Reference,(Date == null ? "" : Date.Value.ToString())).GetHashCode();
}
}
I will be retrieving 2 lists of this class - what I want to do is to compare the two, and get ones that don't exist in both. So if an item exists in x list but not in y, I want to perform an action for the items in this list. If an item exists in y list but not in x, I want to do a different action.
How would I do this? Using LINQ I guess!
EDIT: Performance is not much of an issue - this will only be run once
It sounds like you just want Except:
foreach (var newItem in firstList.Except(secondList))
{
...
}
As an aside:
That's not a terribly nice way of generating a hash code - search for other questions here.
Delegate from Equals(object) to Equals(DocumentCompare) to avoid repetitive logic
Mutable types aren't great candidates for equality comparisons (in particular, one you've used a value as a key in a dictionary, if you change the equality-sensitive components you won't be able to find the key again)
Even if you do want it to be mutable, properties are better for encapsulation than public fields
I would either seal the type or check whether the two objects are exactly the same type, as otherwise you could end up with asymmetric equality
here is the code:
var elementsMissingFromFirstList = firstList.Except(secondList).ToList();
var elementsMissingInSecondList = secondList.Except(firstList).ToList();
now you can perform your actions on these missing elements :)
You can use this method to compare objects of two different Lists. exmp: List and List x and y = DocumentCompare,
public static bool EqualsObject<T>(this T t1, T t2) where T : class
{
var p1 = t1.GetType().Fields();
var p2 = t2.GetType().Fields();
for (int j = 0; j < p1.Length; j++)
{
var x = p1[j].GetValue(t1, null);
var y = p2[j].GetValue(t2, null);
if (x == null && y == null)
continue;
if (x != null && y == null)
return false;
if (x == null)
return false;
if (!x.Equals(y))
{
return false;
}
}
return true;
}
This method will show the difference between these two lists.
public static List<T> DifferentObjects<T>(List<T> t, List<T> t2) where T : class
{
var diff = new List<T>();
if (t != null && t2 != null)
{
foreach (T t1 in t)
{
var state = false;
foreach (T t3 in t2.Where(t3 => EqualsObject(t1,t3)))
{
state = true;
}
if (!state)
{
diff.Add(t1);
}
}
}
return diff;
}
you can use code this way
var t = new List<DocumentCompare>();
var t2 = new List<DocumentCompare>();
t.Add(new DocumentCompare{Customer = "x"});
t.Add(new DocumentCompare{Customer = "y"});
t.Add(new DocumentCompare{Customer = "z"});
t2.Add(new DocumentCompare { Customer = "t" });
t2.Add(new DocumentCompare { Customer = "y" });
t2.Add(new DocumentCompare { Customer = "z" });
var list = DifferentObjects(t, t2);
var list2 = DifferentObjects(t2, t);
you used fields (Customer,FileName etc..) in your class, so that GetType().Fields(); is used in EqualsObject method. if you use property , you should use GetType().Properties(); in EqualsObject method.