I have this code:
public article GetArticleByWebSite(string webSite)
{
using (var context = new ceopolandEntities())
{
return context.article.Where(a => a.WebSite == webSite).First();
}
}
What's the best way to check if article isn't empty before calling First()?
A try catch block or introduce a variable and check how many articles are there?
Try .FirstOrDefault();. It will return null if nothing is found.
Related
I have the following statement that I am trying to use a try-catch block with
var val= db.shops.where(x=>×.id==ID).Select (a=>a.address).First();
I tried following but has many issues won't even compile.
var val=db.shops.Where(x=>
{
try
{
(x.Id==ID).Select(a=>a.address).First();
}
catch(ex)
{
return ex;
}
}
Please let me know how can I handle the exception in this statement Thanks.
Note: writing this question from mobile phone can't format code. Apologize for it.
Everything inside brackets ({ }) need to have 'regular' block syntax, so return is required here:
...
.Where
(x=>
{
try
{
return (x.Id == ID);
}
catch(ex)
{
throw;
}
}
)
.Select(a=>a.address)
.First(); // Or FirstOrDefault if you expect this statement to yield no result.
As you see, the Where is more like a regular statement now. The Select is moved to outside the Where. If you need exception handling in there, you have to do the same as in the Where block now. Last, return ex is probably meant to be throw ex, which should be throw in this case to preserve call stack.
...that I am trying to use try catch block with
I am guessing you probably meant to write FirstOrDefault based on where you want the try/catch. In the sample code you have provided I see no reason to try to make a catch block into one of the lambda statements. The best thing to do would be to simply use FirstOrDefault as that is the reason why you might get an exception in the code shown.
var address = db.shops.FirstOrDefault(x => ×.id == ID)?.Address;
if(address == null)
// nothing was found or address is null, do something else
Or similar code closer to what you had without my "optimization"
var shop = db.shops.FirstOrDefault(x => ×.id == ID);
if(shop == null) {
// nothing was found, do something else
}
var address = shop.address;
The other reason not to use try/catch is that it can't be translated into SQL and the variable name db which is the container for the shops collection which leads me to believe you are using EF or some other ORM. So even if you were to fix the syntax and your code with added try/catch block compiles you will get a run time error later when you execute the lambda.
You should place the try around your original statement:
try
{
var val= db.shops.where(x=>×.id==ID).Select (a=>a.address).First();
}
catch (Exception ex)
{
return ex; //I assume the return type here is wrong. Maybe return null?
}
However, there's nothing about that line that should require a try/catch. Try this:
var val= db.shops.where(x=>×.id==ID).Select(a=>a.address).FirstOrDefault();
The FirstOrDefault will return null if there are no results.
I'm facing a very strange problem on two easy webapi methods:
I have lot of methods that are used to retrive masterdata from db.
They are all similars and they all read tables with same structures.
I really don't know why for example this method works:
this works
[HttpGet]
//[Authorize]
[Route("offertsource/get")]
public IHttpActionResult api_MasterData_OffertSource_GET()
{
var res = new List<mdOffertSource>();
try
{
res = (from c in db.mdOffertSources.OrderBy(x => x.OffertSource)
select new mdOffertSource() { idOffertSource = c.idOffertSource, Code = c.Code, OffertSource = c.OffertSource }).ToList();
return Ok(res);
}
catch (Exception e)
{
return BadRequest(e.Message);
}
}
and this doesn't work:
NOT working code
[HttpGet]
//[Authorize]
[Route("offertstatus/get")]
public IHttpActionResult api_MasterData_OffertStatus_GET()
{
var res = new List<mdOffertStatus>();
try
{
res = (from c in db.mdOffertStatus.OrderBy(x => x.intOrder).ThenBy(x => x.OffertStatus)
select new mdOffertStatus() { idOffertStatus = c.idOffertStatus, Code = c.Code, OffertStatus = c.OffertStatus }).ToList();
return Ok(res);
}
catch (Exception e)
{
return BadRequest(e.Message);
}
}
I have lot of methods similar to the first one working and only the second one below is not working.
If I test it, i get this error:
Explicit construction of entity type 'XionDB.mdOffertStatus' in query is not allowed.
I have already tried to remove the table mdOffertStatus from the dbml file and to add again it but I face the same problem...
This is very strange.
Thanks to support
Your OfferSources table isn't empty, is it? That would cause the Select not to be called and avoid the error thrown in the second method.
(Would leave this as a comment but don't have enough points.)
I solved my problem by deleting the dbml file and adding it again...
Before I tryied to remove and add again the table mdOffertStatus but nothing changed, dropping the dbml and adding it again fixed the problem.
May be there was some mess in the solution...
Thanks to support
What is the proper way to create a variable that will house a list of anonymous objects that are generated through a LINQ query while keeping the variable declaration outside of a try/catch and the assignment being handled inside of a try/catch?
At the moment I'm declaring the variable as IEnumberable<object>, but this causes some issues down the road when I'm trying to use it later...
i.e.
var variableDeclaration;
try{
...
assignment
...
}catch...
EDIT:
If it's relevant (don't think it is) the list of objects is being returned as a Json result from an MVC3 action. I'm trying to reduce the time that some using statements are open with the DB as I'm having some performance issues that I'm trying to clear up a bit. In doing some of my testing I came across this issue and can't seem to find info on it.
EDIT 2:
If I could request the avoidance of focusing on LINQ. While LINQ is used the question is more specific to the scoping issues associated with Anonymous objects. Not the fact that LINQ is used (in this case) to generate them.
Also, a couple of answers have mentioned the use of dynamic while this will compile it doesn't allow for the usages that I'm needing later on the method. If what I'm wanting to do isn't possible then at the moment the answer appears to be to create a new class with the definition that I'm needing and to use that.
It's possible to get around this by creating a generic Cast method as outlined by Jon Skeet here. It will work and give you the intellisense you want. But, at this point, what's wrong with creating a custom type for your linq method?
public class MyClass
{
public int MyInt { get; set; }
}
IEnumerable<MyClass> myClass =
//Some Linq query that returns a collection of MyClass
Well, if you're using LINQ, the query is not evaluated unless materialized...
So, you might be able to:
var myQuery = //blah
try
{
myQuery = myQuery.ToList(); //or other materializing call
}
catch
{
}
Could you perhaps get away with using dynamic ??
dynamic variableDeclaration;
try
{
variableDeclaration = SomeList.Where(This => This == That);
}
catch { }
Not sure what this will affect further in your code block, but just a thought :)
If you are declaring the variable ahead of using it like a try/catch you can't use [var] as it is intendend. Instead you have to type the the variable.
var x = 0;
try{
x = SomethingReturningAnInt();
}
or
int x;
try{
x = SomethingReturningAnInt();
}
However in your case you don't really "know" what the method returns
var x = ...;
try{
x = Something();
}
catch{}
won't work
Option you have when you don't know the type in advance is use of dynamic:
dynamic x;
try{
x = Something();
}
catch{}
(But that feels like going back to VB4)
Another cheat: you can define variable locally (similarly to Jon's hack in Dave Zych answer) and than use it inside try/catch. As long as you can create the same anonymous item type before try-catch you are OK (as anonymous types wit the same field names and types are considered the same):
var myAnonymouslyType = Enumerable.Repeat(
new {Field1 = (int)1, Field2 = (string)"fake"}, 0);
try
{
myAnonymouslyType = ...(item =>
new {Field1 = item.Id, Field2=item.Text})...
}
...
This is safer option than covered in Jon's casting of anonymous types between functions because compiler will immediately find errors if types don't match.
Note: I'd vote for non-anonymous type if you have to go this way...
Note 2: depending on your actual need consider simply returning data from inside try/catch and having second return of default information outside.
This has vexed me for a while. In the end I've build some Generic helper methods where I can pass in the code that generates the anonymous objects, and the catch code as lamdas as follows
public static class TryCatch
{
public static T Expression<T>(Func<T> lamda, Action<Exception> onException)
{
try
{
return lamda();
}
catch(Exception e)
{
onException(e);
return default(T);
}
}
}
//and example
Exception throwexception = null;
var results = TryCatch.Expression(
//TRY
() =>
{
//simulate exception happening sometimes.
if (new Random().Next(3) == 2)
{
throw new Exception("test this");
}
//return an anonymous object
return new { a = 1, b = 2 };
} ,
//CATCH
(e) => { throwexception = e;
//retrow if you wish
//throw e;
}
);
https://gist.github.com/klumsy/6287279
I am having this Linq To SQL query which is taking Customer Category from database.The CustCategory will be defined already.Here is the query.
public IList<string> GetAccountType()
{
using (var db = new DataClasses1DataContext())
{
var acctype = db.mem_types.Select(account=>account.CustCategory).Distinct().ToList();
if (acctype != null)
{
return acctype;
}
}
}
Currently I am getting an error that Not all code paths return a value.If I am always certain that the value is there in the database then do I need to check for null,If I need to check for null then how do I handle this.
Can anyone help me with this.
Any suggestions are welcome.
Since Enumerable.ToList never returns null (see the Return Value section of the documentation), you can safely remove the if.
EDIT: Note that, no matter what your database contains, acctype will never be null:
If no value is found in the database, the return value will be an empty list (which is different than null).
If one record is found and its value is null, the return value will be a valid list with one entry, whose value is null. Still, the list itself is not null.
What happens if:
if (acctype != null)
Is null? What is your method supposed to return?
You need to return something
This is not about LINQ to SQL, the method GetAccountType() must return IList<string>. You should return return acctype; and then check this returned list later using Any(), something like:
if(GetAccountType.Any()){
//not empty
}
How about something like this for a fairly clean and readable solution?:
(Note, updated: removed the check for null, since it would clearly not have any effect).
public IList<string> GetAccountType()
{
var acctype = new List<string>();
using (var db = new DataClasses1DataContext())
{
acctype = db.mem_types.Select(
account=>account.CustCategory).Distinct().ToList();
}
return acctype;
}
You need to return a value from your function:
public IList<string> GetAccountType()
{
using (var db = new DataClasses1DataContext())
{
var acctype = db.mem_types.Select(account=>account.CustCategory).Distinct().ToList();
if (acctype != null)
{
return acctype;
}
}
return acctype;
}
I've posted a code sample below. Firstly let me explain
termStore.Groups in the code below is a collection of Group Objects (The exact class is irrelevant).
Checking for null : if (termStore.Groups[groupName] == null) seems like a logical (clean) approach, but if the Groups collection is empty then an exception is produced.
using the termStore.Groups.Contains is not an option either because this expects a strong type i.e: .Contains(Group)... not .Contains(GroupName as string)
Can someone recommend a clean / generic way I can check for if an item exists in collection .
Thank you....
TermStore termStore = session.TermStores.Where(ts => ts.Name == termStoreName).FirstOrDefault();
if (termStore.Groups[groupName] == null)
{
termStore.CreateGroup(groupName);
termStore.CommitAll();
}
Update: The exact class Sharepoint Taxonomy Classes. http://msdn.microsoft.com/en-us/library/microsoft.sharepoint.taxonomy.group.aspx
Update 2, the exact collection : http://msdn.microsoft.com/en-us/library/microsoft.sharepoint.taxonomy.groupcollection.aspx
Microsoft.SharePoint.Taxonomy.GroupCollection implements IEnumerable<Group>, so a bit of LINQ is probably just what the doctor ordered:-
if(termStore.Groups.Any(x => x.Name == "MyGroup"))
{
// group contains at least one item matching the predicate.
}
else
{
// group contains no items matching the predicate.
}
You'll need to be using .NET 3.5 or better and add "using System.Linq;" to the top of your file.
Edit
If you don't have LINQ available, or if it offends you, or if you've genuinely profiled and found that iterating over Groups is killing performance compared to the string indexer, you could use GroupCollection.Count to avoid the error state:-
if (termStore.Groups.Count == 0 || termStore.Groups[groupName] == null)
{
// Group doesn't exist.
}
IEnumerable.Any(...) should work for your case:
termsStore.Groups.Any()
I think this is what you are looking for:
termStore.Groups.ContainsKey(groupName)
Checks that the key exists, doesn't throw an exception if it doesn't. This is assuming that Groups is a collection that implements IDictionary.
May be this
termStore.Any() && termStore.Groups.Any() && termStore.Groups[groupName] == null
Ok, 2nd attempt. If Groups doesn't contain the required ContainsKey method then you can write it yourself. Then you can just use ContainsKey in place of Contains.
static class GroupExtensions
{
public static bool ContainsKey(this Groups groups, string key)
{
try
{
if(groups[key] == null)
{
return false;
}
}
catch
{
return false;
}
return true;
}
}