I have this linq query, that is doing a select with loads of joins, the query has to return this, and I need to check a "splitted" string for a certain other string. My query is the following:
....
where
&& Name.Split(',').Contains(container) == true
))
select new
{
...
});
But this gives me an exception, because of the split method. What can I do? I tried the Any clause, but still gives me an error...
Thanks in advance :)
Related
I scratched my head for one hour on this yesterday with no results but sweat.
string SearchTag = "";
Extension.getDBService<MyClass>().FindAll(i => <true condition>);
This returned me all my MyClass DB records as I would expect.
string SearchTag = "";
Extension.getDBService<MyClass>().FindAll(i => <true condition> && i.TAG.ToLower().Trim().Contains(SearchTag.ToLower().Trim()));
This returned a 0 Count collection!! I do not understand this.
string SearchTag = "e";
Extension.getDBService<MyClass>().FindAll(i => <true condition> && i.TAG.ToLower().Trim().Contains(SearchTag.ToLower().Trim()));
This returns a collection containing all MyClass DB records again. This is normal as i.TAG always contains "e".
Why do I get a 0 members collection with the second expression?
"string".Contains("") should always be true right?
PS: Extension.getDBService() is a call to a DBContext by the way.
Thx for your assistance.
Interestingly, the way you wrote the LINQ query generates SQL CHARINDEX(...) > 0 criteria which returns false for empty string.
However, if you remove (move outside the query) the ToLower().Trim() part of the SearchTag variable
SearchTag = SearchTag.ToLower().Trim();
and use
i.TAG.ToLower().Trim().Contains(SearchTag)
inside the LINQ query, then the generated SQL criteria is LIKE operator and works as expected.
Just another example that LINQ to Entities is not like LINQ to Objects.
I would like to concatenate a string using lambda to compare that concatenated value against a certain condition.
Invoices = Invoices.Where(f => ((string)f.invoice_prefix + String.Format("{0:0000}", Convert.ToInt32(f.invoice_number))).ToLower().Equals(condition7));
But I get an error message :
The name 'f' does not exist in the current context
Tried several String.Format and String.Concat variants like
Invoices = Invoices.Where(f => (String.Format("{0}{1}",f.invoice_prefix,String.Format("{0:0000}", Convert.ToInt32(f.invoice_number)))).ToLower().Equals(condition7));
but no success... Can somebody help me with the syntax?
Thanks in advance!
Linq to Entities doesn't understand all of the .NET framework methods.
In order to run this as a SQL statement on the database, you need to only use operators that can be converted to SQL. That means you need to re-write your predicate using primitive data types.
So something like this:
string prefixCondition = ...
int invoiceNumberCondition = ...
Invoices.Where( f =>
f.invoice_prefix == prefixCondition
&&
f.invoice_number == invoiceNumberCondition
)
I recommend using LinqPad to test with, as it shows you the generated SQL statement.
I want to query my item in table Items, where the last update of each item must be less than 91 days old (from last update till now) and the quantity > 0.
This is my code in the Model:
public IList<Item> GetAllProducts()
{
var ien_item = from i in this.DataContext.Items
orderby i.LastUpdated descending
select i;
return ien_item.ToList().Where(
s =>
HelperClasses.HelperClass.IsLastUpdate(s.LastUpdated.Value) == true
&&
(s => s.Quantity) > 0
)
.ToList();
}
Anyone can solve it? Thanks.
We don't really know what's not working here. EDIT: Merlyn spotted it; your lambda syntax is messed up. There's more to do here though.
However, I'd have thought you'd want this:
public IList<Item> GetAllProducts()
{
var lastUpdateLimit = DateTime.UtcNow.Date.AddDays(-91);
var query = from item in DataContext.Items
where item.Quantity > 0 && item.LastUpdated >= lastUpdateLimit
orderby item.LastUpdated descending
select item;
return query.ToList();
}
Note that this is able to do all the querying at the database side instead of fetching all the items and filtering at the client side. It does assume that HelperClasses.HelperClass.IsLastUpdate is simple though, and basically equivalent to the filter I've got above.
(One additional point to note is that by evaluating UtcNow.Date once, the result will be consistent for all items - whereas if your code evaluates "today" on every call to IsLastUpdate, some values in the query may end up being filtered against a different date to other values, due to time progressing while the query is evaluating.)
EDIT: If you really need to use HelperClasses.HelperClass.IsLastUpdate then I'd suggest:
public IList<Item> GetAllProducts()
{
var query = from item in DataContext.Items
where item.Quantity > 0
orderby item.LastUpdated descending
select item;
return query.AsEnumerable()
.Where(s => HelperClass.IsLastUpdate(s.LastUpdated.Value))
.ToList();
}
... then at least the quantity filter is performed at the database side, and you're not creating a complete buffered list before you need to (note the single call to ToList).
The problem is your lambda syntax. You're trying to define a second lambda while in the middle of defining a first lambda. While this is possible to do, and useful in some contexts, it is sort of an advanced scenario, and probably won't be useful to you until you know you need it.
Right now, you don't need it. Unless you know you need it, you don't need it :)
So -
Instead of what you've written:
.Where(
s =>
HelperClasses.HelperClass.IsLastUpdate(s.LastUpdated.Value) == true
&& (s => s.Quantity) > 0
)
Write this instead:
.Where(
s =>
HelperClasses.HelperClass.IsLastUpdate(s.LastUpdated.Value) == true
&& s.Quantity > 0 // Notice I got rid of the extra lambda here
)
If you're morbidly curious:
The compile error you got is because you didn't define your second lambda correctly. It redefined a variable you'd already used (s), and you were trying to check if a lambda was greater than zero. That makes no sense. You can only compare the result of a lambda to some value. It's like calling a function. You don't compare functions to numbers - you compare the result you get when calling a function to a number.
Easy ...
public IList<Item> GetAllProducts()
{
var ien_item =
from i in DataContext.Items
where
HelperClasses.HelperClass.IsLastUpdate(i.LastUpdated.Value)
&& s.Quantity > 0
orderby i.LastUpdated descending
select i;
return ien_item.ToList();
}
Linq to SQL: Methods are not allowed (linq is not magic and can not convert C# methods to TSQL)
http://msdn.microsoft.com/en-us/library/bb425822.aspx
Linq to Object: while looking the same, it is much more powerful than linq to SQL... but can not query SQL databases :)
http://msdn.microsoft.com/en-us/library/bb397919.aspx
Linq to XML: same as linq to Object, with xml object
http://msdn.microsoft.com/en-us/library/bb387098.aspx
Linq to Dataset: not the same as Linq to SQL !
http://msdn.microsoft.com/en-us/library/bb386977.aspx
Other linq providers:
http://en.wikipedia.org/wiki/Language_Integrated_Query
I'm using a LINQ to Entities, and I have a couple of queries for which I want to be able to specify the Select clause at runtime.
I figured I'd have to do it by building an Expression and adding it to the IQueryable, but I'm not sure how to do this. Can anybody give me a hint?
I am not sure you could do what you want with expressions. The select clause specifies the type of the object in the IQueryable collection, that has to be defined at compile time. There is something called Dynamic Linq that can do what you want.
Something like this:
IQueryable<cerberus_Ticket> matches = db.cerberus_Tickets;
if (this.AgentIdField.Text.Trim().Length > 0)
{
matches = matches.Where(a => a.AgentId == criteria.AgentId);
}
if (this.TicketIdField.Text.Trim().Length > 0)
{
matches = matches.Where(a => a.TicketId.Contains(criteria.TicketId));
}
var output = matches.ToList();
The LINQ-to-SQL query in Visual Studio generates an SQL query with errors. In LINQPad, the same LINQ query using the same database (or DataContext) runs just fine.
LINQ Query
var accesDomaines = from t in db.Access
where t.IdUser == access.IdUtilisateur
where t.IdDomain != null
where t.IdRole == access.IdRole
where t.IdPlace == access.IdPlace
select t;
Here's a small part of generated SQL where the error occurs:
WHERE (...) AND ([t3].[IdRole] = ) AND (...)
After the equals in where clause, there's literally nothing ! In the SQL query of LINQPad we see the good where clause:
WHERE (...) AND ([t3].[IdRole] IS NULL) AND (...)
When I compare the two generated SQL queries from VS and LINQPad, line by line, this is the same thing. Except LINQPad is using params and also the missing right part of equal in where clause of Visual Studio, as shown before.
Note 1
In the LINQ query, I tried with this syntax in where clauses:
where t.IdRole.Equals(acces.IdRole.Value)
But also generates a bad result. I even tried something like this before the LINQ query:
if (!acces.IdRole.HasValue) { acces.IdRole = null; }
Note 2
Properties are nullable integers. I do want null in query if property is null. Obviously, I want the value of property if there's a value.
Note 3
I have tried the proposition made in this question: Linq where column == (null reference) not the same as column == null
...with no success.
Any explanation of two similar LINQ queries, but generating a good and a bad SQL query? Any suggestion to solve this problem?
Thank you!
try this:
where object.Equals(t.IdRole, access.IdRole)
Use
object.Equals()
.Net would take care of generating correct sql for null condition.
Example:
Say you have a street table with columns like Suffix and Prefix. Then following linq query doesn't work:
string suffix = "ST";
string prefix = null;
var map = from s in Streets
where s.Suffix==suffix || s.Prefix==prefix
select s;
It would generate following sql:
SELECT [t0].[StreetId], [t0].[Prefix], [t0].[Suffix]
FROM [Street] AS [t0]
WHERE ([t0].[Suffix] = #p0) AND ([t0].[Prefix] = #p1)
we can clearly see it will not return any result.
Using object.Equals():
string suffix = "ST";
string prefix = null;
var map = from s in Streets
where object.Equals(s.Suffix, suffix) && object.Equals(s.Prefix,prefix)
select s;
would generate sql:
SELECT [t0].[StreetId], [t0].[Prefix], [t0].[Suffix]
FROM [Street] AS [t0]
WHERE ([t0].[Suffix] IS NOT NULL) AND ([t0].[Suffix] = #p0)
AND ([t0].[Prefix] IS NULL)
Which is correct one.
(Little late, but wanted to expand the answer for the benefit of others)
Have you tried verifying whether your properties had values with the HasValues property provided by the Nullables?
where t.IdRole == access.IdRole.HasValues ? access.IdRole.Value : null
Perhaps this could work. I haven't used LINQ-to-SQL really.
This example worked for me:
var aff3 = from a in context.Affiliates
where ((name == null && a.CompanyName == null) || (a.CompanyName == name))
select a.ID;