How do I write something like this:
int result = database
.Where(x => x.Name == "Criteria")
.Sum(x => x.Count)) ?? 0;
Where it will return the sum value unless linq does not find anything in which case it will return 0.
EDIT: The field is not null-able.
EDIT 2: I am using Entity Framework.
You were very close with your original query. You only needed to cast your Count variable:
int result = database
.Where(x => x.Name == "Criteria")
.Sum(x => (int?)x.Count) ?? 0;
Doing it this way would be a little more efficient and elegant than wrapping it in a Try/Catch.
I suspect you are using Entity Framework. If you were just using Linq-to-Objects, the solutions everybody else have provided would have worked.
This should work fine (no need for ?? 0):
var result = database
.Where(x => x.Name == "Criteria")
.Sum(x => x.Count))
Unless you want to check if x itself is null or not:
var result = database
.Where(x => x != null)
.Where(x => x.Name == "Criteria")
.Sum(x => x.Count))
You can just write:
int result = database
.Where(x => x.Name == "Criteria")
.Sum(x => x.Count));
The Enumerable.Sum method already returns zero on no results. From the documentation:
returns zero if source contains no elements.
This should work just fine:
var result = database.Where(x => x.Name == "Criteria").Sum(x => x.Count));
If no elements are returned by the Where function then the Sum function will return 0.
All of the Linq functions that return an IEnumerable<T> will return an empty collection instead of null.
Use the Aggregate extension method where 0 is a seed value
int sum = database.Where(x=>x.Name == "Criteria")
.Aggregate(0, (total, next) => total +=next);
I did it in a way that no one is going to like but garrantee to work 100% of the time, behold!
int result = 0;
try{
result = database
.Where(x => x.Name == "Criteria")
.Sum(x => x.Count));
} catch (Exception e){ }
Related
As shown in the below code, the API will hit the database two times to perform two Linq Query. Can't I perform the action which I shown below by hitting the database only once?
var IsMailIdAlreadyExist = _Context.UserProfile.Any(e => e.Email == myModelUserProfile.Email);
var IsUserNameAlreadyExist = _Context.UserProfile.Any(x => x.Username == myModelUserProfile.Username);
In order to make one request to database you could first filter for only relevant values and then check again for specific values in the query result:
var selection = _Context.UserProfile
.Where(e => e.Email == myModelUserProfile.Email || e.Username == myModelUserProfile.Username)
.ToList();
var IsMailIdAlreadyExist = selection.Any(x => x.Email == myModelUserProfile.Email);
var IsUserNameAlreadyExist = selection.Any(x => x.Username == myModelUserProfile.Username);
The .ToList() call here will execute the query on database once and return relevant values
Start with
var matches = _Context
.UserProfile
.Where(e => e.Email == myModelUserProfile.Email)
.Select(e => false)
.Take(1)
.Concat(
_Context
.UserProfile
.Where(x => x.Username == myModelUserProfile.Username)
.Select(e => true)
.Take(1)
).ToList();
This gets enough information to distinguish between the four possibilities (no match, email match, username match, both match) with a single query that doesn't return more than two rows at most, and doesn't retrieve unused information. Hence about as small as such a query can be.
With this done:
bool isMailIdAlreadyExist = matches.Any(m => !m);
bool isUserNameAlreadyExist = matches.LastOrDefault();
It's possible with a little hack, which is grouping by a constant:
var presenceData = _Context.UserProfile.GroupBy(x => 0)
.Select(g => new
{
IsMailIdAlreadyExist = g.Any(x => x.Email == myModelUserProfile.Email),
IsUserNameAlreadyExist = g.Any(x => x.Username == myModelUserProfile.Username),
}).First();
The grouping gives you access to 1 group containing all UserProfiles that you can access as often as you want in one query.
Not that I would recommend it just like that. The code is not self-explanatory and to me it seems a premature optimization.
You can do it all in one line, using ValueTuple and LINQ's .Aggregate() method:
(IsMailIdAlreadyExist, IsUserNameAlreadyExist) = _context.UserProfile.Aggregate((Email:false, Username:false), (n, o) => (n.Email || (o.Email == myModelUserProfile.Email ? true : false), n.Username || (o.Username == myModelUserProfile.Username ? true : false)));
I want to display results that don't have a secondary ID displayed first and then display items that do have a secondary ID. But then I need to Skip and Take.
IQueryable<thing> result;
IQueryable<thing> result2;
result2 = result
.Where(t => !(t.second_id == null || t.second_id.Trim() == string.Empty))
.OrderBy(t => t.second_id);
result = result
.Where(t => (t.second_id== null || t.second_id.Trim() == string.Empty))
.OrderBy(t => t.first_id);
result = result.Concat(result2);
return result
.Select(t => t.primary_key)
.Skip(pageSize * pageNumber)
.Take(pageSize)
.ToList();
The problem is that after Concat the IQueryable is no longer technically ordered so Skip and Take throw an error. Like this:
PagedList error: The method 'OrderBy' must be called before the method 'Skip'
You can do it in one query with the conditional operator:
return result.OrderBy(t => (t.second_id != null && t.second_id.Trim() != String.Empty))
.ThenBy(t => (t.second_id != null && t.second_id.Trim() != String.Empty) ? t.second_id : t.first_id)
.Select(t => t.primary_key)
.Skip(pageSize * pageNumber)
.Take(pageSize)
.ToList();
It would need some adjustment if you need to order duplicate second_id in some way, but your original code doesn't.
PS I folded in the negation operator since I think it reads more clearly.
You can do the job with a single query
result = result
.OrderByDescending(t => (t.second_id== null || t.second_id.Trim() ==
string.Empty))
.ThenBy(t => t.second_id)
.ThenBy(t => t.first_id)
.Select(t => t.primary_key)
.Skip(pageSize * pageNumber)
.Take(pageSize)
.ToList();
I have this LINQ to entity:
int siteNumbers = g.Select(x => x.siteId).ToArray().Distinct().Count()
For example:
When x.siteId is -1 I don't want the value to be counted,i.e I want to count only values that not equal to -1.
when x:[1,2,6,-1] then siteNumbers value is 3.
when x:[-1] then siteNumbers value is 0.
What do I have to change in query above to implement it?
You can take advantage of the Where clause in LINQ:
int siteNumbers = g.Where(x => x.siteId != -1)
.Select(x => x.siteId)
.Distinct()
.Count();
You can also remove the .ToArray() as it is redudant.
Working example:
https://ideone.com/LvOe0i
Use Where to filter the result
int siteNumbers = g.Where(x => x.siteId != -1)
.Select(x => x.siteId)
.Distinct()
.Count();
Also calling ToArray might not be necessary since siteId is integral and SQL knows who to compare them and get distinct values.
you can also add a condition to Count
int siteNumbers = g.Select(x => x.siteId)
.Distinct()
.ToArray()
.Count(x => x != -1);
you should call ToArray since Count overload with predicate is not supported by linq to entities
You can add a Where statement before Select statement like that:
int siteNumbers = g.Where(x => x.siteId != -1).Select(x => x.siteId).ToArray().Distinct().Count()
You can use a where clause in your query to filter out data with siteId == -1
int siteNumbers = g.Where(f => f.siteId != -1)
.Select(x => x.siteId)
.Distinct()
.Count();
Also notice, you do not need a ToArray() for this.
Try this
int siteNumbers = g.Select(x=>x.siteId).Where(i => i != -1).Distinct().Count()
I've tried some combinations but I just don't understand how to do the following:
Lets say I have tables Requests and RequestActivities. I need to get all request sorted by RequestActivity.TimeOfCreation in descending order but RequestActivity may be null.
List<DA.GeneralRequest> ongoingGeneralRequests = db.GeneralRequests
.Where(t => t.GeneralRequestStatusID != 3 && (t.SupervisorID == currentUserId || t.CreatorID == currentUserId || t.AssignedUsers.Any(au => au.UserID == currentUserId)))
.OrderByDescending(x => x.GeneralRequestActivities.OrderBy(ga => ga.GeneralRequestActivityDate).Last().GeneralRequestActivityDate) //gives exeption
.ThenBy(a => a.Deadline).ToList();
I'm not really familiar with LINQ-To-SQL but doesn't work MAX in this case?
.OrderByDescending(x => x.GeneralRequestActivities
.Max(ga => ga.GeneralRequestActivityDate))
.ThenBy(a => a.Deadline)
.ToList();
You need to first cache the ordering value, and then order by the date if it is not null, else by some default date you want:
List<DA.GeneralRequest> ongoingGeneralRequests = db.GeneralRequests
.Where(t => t.GeneralRequestStatusID != 3 && (t.SupervisorID == currentUserId || t.CreatorID == currentUserId || t.AssignedUsers.Any(au => au.UserID == currentUserId)))
.Select(x => new {
Value = x,
OrderByValue = x.GeneralRequestActivities
.OrderBy(ga => ga.GeneralRequestActivityDate)
.LastOrDefault()) // cache value
.OrderByDescending(x => x.OrderByValue != null ?
OrderByValue.GeneralRequestActivityDate
: some default value)
.ThenBy(a => a.Value.Deadline)
.Select(a => a.Value)
.ToList();
Note that you can't use Last() extension method on empty IEnumerable. This is why you get the exception:
InvalidOperationException : The source sequence is empty.
In this line:
x.GeneralRequestActivities.OrderBy(ga => ga.GeneralRequestActivityDate).Last()
x.GeneralRequestActivities is empty, so calling Last() on it result on the exception.
Instead, use the LastOrDefault() extension method, which return null if the IEnumerable is empty.
Return Value Type: TSource default (TSource) if the source sequence is
empty; otherwise, the last element in the IEnumerable.
About the homework:
There are casters(witch(0)/fairy(1)) and they have spellpower(int). I stored them in a list.
I'm to find the best of both types. (There can be multiple casters with the same spellpower)
I've come up with this code, but there is a problem. If the caster with the most spellpower is a 1, then the first FindAll won't return anything, because it tries to find the caster with type 0 AND with the most spellpower. How can I get a list containing type 0 caster(s) with the most spellpower, if the caster with the most overall spellpower is type 1?
private List<Caster> BestCasters()
{
List<Caster> temp = new List<Caster>();
temp = casters.FindAll(x => x.SpellPower == casters.Max(y => y.SpellPower) && (x.TypeOfCaster == 0));
temp.AddRange(casters.FindAll(x => x.SpellPower == casters.Max(y => y.SpellPower) && (x.TypeOfCaster == 1)));
temp.OrderBy(x => x.TypeOfCaster).ThenBy(y => y.CasterName);
return temp;
}
The LINQ GroupBy behavior is perfect for this:
var strongest_casters = casters.GroupBy(c => c.TypeOfCaster)
.Select(grp => grp.OrderByDescending(x => x.SpellPower)
.First()
);
Or to return more than one of each type:
var strongest_casters = casters.GroupBy(c => c.TypeOfCaster)
.SelectMany(grp => grp.Where(y.SpellPower == grp.Max(x => x.SpellPower))
);
private List<Caster> BestCasters()
{
var witches = casters.Where(x => x.TypeOfCaster == 0).ToList();
var fairies = casters.Where(x => x.TypeOfCaster == 1).ToList();
int witchesMax = witches.Max(x => x.SpellPower);
int fairiesMax = fairies.Max(x => x.SpellPower);
var temp = witches.Where(x => x.SpellPower == witchesMax).ToList();
temp.AddRange(fairies.Where(x => x.SpellPower == fairiesMax));
return temp.OrderBy(x => x.TypeOfCaster).ThenBy(y => y.CasterName).ToList();
}
If you have to use FindAll like this you should invoke the Max on a subset only containing the casters of the right kind. Of course it would make more sense to split the initial list first and then fetch the strongest caster of each kind.
Since you did not tell what exactly you have to do I can only hope that you are allowed to split :-)