I am new to EF and LINQ, hoping to get some answers here.
I am trying to search from list with where condition that is according to the selecteditem from a combobox.
The combobox has 15 items(all bit datatypes) but let me just narrow it down to 2 for examples sake. items are( pro bono, civil)
Now I have a list called listOfAllNeutrals (object name is Neutral with properties such as pro bono (bit) and civil(bit), and I want to filter it using the where condition according to the selected item.
so if selected item = pro bono, the linq would look like this
var result = from n in listOfAllNeutrals
where n.probono==true
select n;
but my prob is how do I tell that the n.property should be according to the selecteditem?
like this:
var result = from n in listOfAllNeutrals
where getpropertyName==true
select n;
is there a simpler way, I don't want to use If conditions if possible.
You need to use if's or switch inside the getpropertyName(Neutral objNeutral) function to Map the selected item to the property you want to evaluate and evaluate it. You need to map object => property in some way.
Try
var result = from n in listOfAllNeutrals
where (selectedItem == proBono && n.probono == true)
|| (selectedItem == civil && n.civil == true)
select n;
Related
I want to extract part of a collection to another collection.
I can easily do the same using a for loop, but my linq query is not working for the same.
I am a neophyte in Linq, so please help me correcting the query (if possible with explanation / beginners tutorial link)
Legacy way of doing :
Collection<string> testColl1 = new Collection<string> {"t1", "t2", "t3", "t4"};
Collection<string> testColl2 = new Collection<string>();
for (int i = 0; i < newLength; i++)
{
testColl2.Add(testColl1[i]);
}
Where testColl1 is the source & testColl2 is the desired truncated collection of count = newLength.
I have used the following linq queries, but none of them are working ...
var result = from t in testColl1 where t.Count() <= newLength select t;
var res = testColl1.Where(t => t.Count() <= newLength);
Use Enumerable.Take:
var testColl2 = testColl1.Take(newLength).ToList();
Note that there's a semantic difference between your for loop and the version using Take. The for loop will throw with IndexOutOfRangeException exception if there are less than newLength items in testColl1, whereas the Take version will silently ignore this fact and just return as many items up to newLength items.
The correct way is by using Take:
var result = testColl1.Take(newLength);
An equivalent way using Where is:
var result = testColl1.Where((i, item) => i < newLength);
These expressions will produce an IEnumerable, so you might also want to attach a .ToList() or .ToArray() at the end.
Both ways return one less item than your original implementation does because it is more natural (e.g. if newLength == 0 no items should be returned).
You could convert to for loop to something like this:
testColl1.Take(newLength)
Use Take:
var result = testColl1.Take(newLength);
This extension method returns the first N elements from the collection where N is the parameter you pass, in this case newLength.
I m trying to select a column's value from a datatable based on conditions.
var results = from DataRow myRow in dtCallBack.AsEnumerable()
where myRow.Field<DateTime>(1) == startDateTime
&& myRow.Field<int>(0) == callBackID
select myRow.Field<int>(3);
My datatable contains 4 columns ID,Date1,Date2,IntVal
I want to convert the variable results to int. (I want to return the column 4 IntVal)
var results = (from DataRow myRow in dtCallBack.AsEnumerable
where myRow.Field<DateTime>(1) == startDateTime
&& myRow.Field<int>(0) == callBackID
select myRow.Field<int>(3)).SingleOrDefault();
Well you've currently got an IEnumerable<int> by the looks of it. So which of those results do you want? What do you want to happen if there aren't any results?
If you're confident there's only a single result, you can use:
var result = results.Single();
If you want the first result or 0 if there aren't any, you could use
var result = results.FirstOrDefault();
If you want the first result and an exception if there aren't any, you could use
var result = results.First();
Basically there are lots of options, and you'll need to clarify your requirements before we can really give you a more concrete answer.
I've got a list of IQueryable. I'm trying to split this list into an array of IQueryable matching on a certain field (say fieldnum) in the first list...
for example, if fieldnum == 1, it should go into array[1]. I'm using Where() to filter based on this field, it looks something like this:
var allItems = FillListofMyObjects();
var Filtered = new List<IQueryable<myObject>(MAX+1);
for (var i = 1; i <= MAX; i++)
{
var sublist = allItems.Where(e => e.fieldnum == i);
if (sublist.Count() == 0) continue;
Filtered[i] = sublist;
}
however, I'm getting the error Field "t1.fieldnum" is not a reference field on the if line. stepping through the debugger shows the error actually occurs on the line before (the Where() method) but either way, I don't know what I'm doing wrong.
I'm farily new to LINQ so if I'm doing this all wrong please let me know, thanks!
Why don't you just use ToLookup?
var allItemsPerFieldNum = allItems.ToLookup(e => e.fieldnum);
Do you need to reevaluate the expression every time you get the values?
Why not use a dictionary?
var dictionary = allItems.ToDictionar(y => y.fieldnum);
Hello – I’m trying to get a where condition to apply to a sub collection. I can get the criteria to return the proper parents. However, I want the sub collection to be limited to the criteria as well.
In my example code, I only want people with “LINK” skills; also, I only want the skills for each person to equal “LINK.” That is, each person should only have “LINK” for their skills.
Thanks in advance.
List<Skill> skills = new List<Skill>();
skills.Add(new Skill(){SkillName="ASP.NET"});
skills.Add(new Skill(){SkillName="C#"});
Person p1 = new Person(){ Name="Me", Skills=skills} ;
List<Skill> skills2 = new List<Skill>();
skills2.Add(new Skill(){SkillName="ASP.NET"});
skills2.Add(new Skill(){SkillName="C#"});
skills2.Add(new Skill(){SkillName="LINQ"});
Person p2 = new Person(){ Name="You", Skills=skills2} ;
List<Person> People = new List<Person>();
People.Add(p1);
People.Add(p2);
var oResult = (from item in People
from sk in item.Skills
where sk.SkillName == "LINQ"
select item
).ToList();
When I run this. I get p2 (correct), but I want the skills of P2 to only equal LINQ
Do this:
var oResult = (from item in People
where item.Skills.Count() == 1 &&
item.Skills.Any(s => s.SkillName == "LINQ")
select item
).ToList();
This query will return nothing because p2 (You) has other skills in addition to LINQ.
You can do what you want this way:
foreach (var person in oResult)
{
person.Skills.RemoveAll(s => !s.SkillName.Equals("LINQ"));
}
Note: while using LINQ you're only filtering your data. To post process it you use something like the foreach I show you above.
Try this:
var oResult = (from item in People
where item.Skills != null
where item.Skills.Count() > 0
where item.Skills.All(s => s.SkillName == "LINQ")
select item
).ToList();
Even though your example shows that the Skills collection has a value, you want to make sure that your code doesn't blow up if the Skills property is null.
Also, the All predicate returns true if your list is empty so you need to ensure that it is not empty. The above query reads better, but depending on the implementation of the Skills property calling Count() may cause the entire collection to be iterated. You could use Any() instead to ensure that the collection is not empty.
var oResult = (from item in People
where item.Skills != null
where item.Skills.Any()
where item.Skills.All(s => s.SkillName == "LINQ")
select item
).ToList();
How to filter my datagridview by the value of my label.text on click event? That value is from my linq query:
dataSet.Tables[0].AsEnumerable().Where(c => c.Field<int>("ageColumn") > 3 &&
c.Field<int>("ageColumn") < 5).Count();
Let's just say the above query gives me 12 (label.text = 12), now when I click "12", I want my datagridview to ONLY show those 12 rows that meet my above query.
Do you need it to be dynamic? Perhaps store the query itself as a lambda in the Tag property of your label:
Predicate<DataColumn> clause = c => c.Field<int>("ageColumn") > 3
&& c.Field<int>("ageColumn") < 5;
label1.Tag = clause;
... then re-evaluate your query when the label is clicked:
var clause = (sender as Label).Tag as Predicate<DataColumn>;
myDataSource = dataSet.Tables[0].AsEnumerable().Where(clause);
I don't know if this would work, but at least it would let you "attach" a where-clause to various lables.
I'd also recommend taking a look at Bindable LINQ so the results of your queries can be bound to. Very cool stuff.
Now I do not use LINQ, but logic would suggest that whatever is retured by the expression
dataSet.Tables[0].AsEnumerable().Where(c => c.Field<int>("ageColumn") > 3 &&
c.Field<int>("ageColumn") < 5)
Contains the data you seek? Is there not a property in there to enumerate the data?