Good day!
I have this query as shown below:
jt.SummarySpecs.Where(
x => true
)
.FirstOrDefault()
.DocSpecs
.Where(
x => x.DocID == x.DocID
)
.FirstOrDefault()
.FinishingOptionsDesc[0] = option;
But when the code get executed, value for finishingOptionsDesc[0] is not updating...
what's wrong with the query above?
The classes attributes:
"SummarySpecs.cs"
public DocSpec[] DocSpecs { get; set; }
"DocSpecs.cs"
public string[] FinishingOptionsDesc { get; set; }
My only concern is to update the FinishingOptionDesc 1st string.
Thanks
That error means something is null. You have 4 unchecked places in one statement where there could be a null return value. Either of the calls to FirstOrDefault could return null if those collections were empty. Or DocSpecs could be null on the returned object, or FinishingOptionsDesc could be null.
Ideally you'd break this statement up a bit and insert null checks. You could say that you know none of these points should ever be null. If that is the case it may be valid to allow an exception to occur, but arguably it is still worth breaking up the statement to get better error reporting on where the exception occurred.
Try something like this..
UPDATE
if(jt.SummarySpecs.Select(a=>a.DocSpecs).Any())
{
var docSpecs = jt.SummarySpecs.Select(a => a.DocSpecs)
docSpecs.FinishingOptionsDesc[0] = option;
}
Related
I am facing a problem in searching a exact record by LINQ query method in ASP.NET Web API my controller. This is my code:
[HttpGet]
[Route("api/tblProducts/AllProductbySearch/{SearchText}")]
[ResponseType(typeof(IEnumerable<tblProduct>))]
public IHttpActionResult AllProductbySearch(string SearchText)
{
IEnumerable<tblProduct> tblProduct = db.tblProducts.Where(x=>x.PrdKeyword.Contains(SearchText)).AsEnumerable();
if (tblProduct == null)
{
return NotFound();
}
return Ok(tblProduct);
}
In this I am searching the record with value have keyword column and getting the result but problem is that it is not giving exact result for example if in database two record have keyword column value like shirt and another have Tshirt
Then if I pass shirt in SearchText or pass tshirt in SearchText it is giving both record while I want one record which exact match with SearchText. Please help me
My updated action method code is:
[HttpGet]
[Route("api/tblProducts/AllProductbySearch/{SearchText}")]
[ResponseType(typeof(IEnumerable<tblProduct>))]
public IHttpActionResult AllProductbySearch(string SearchText)
{
IEnumerable<tblProduct> tblProduct = db.tblProducts.Where(x => CheckWord(x.PrdKeyword, SearchText)).AsEnumerable();
if (tblProduct == null)
{
return NotFound();
}
return Ok(tblProduct);
}
private bool CheckWord(string source, string searchWord)
{
var punctuation = source.Where(Char.IsPunctuation).Distinct().ToArray();
var words = source.Split().Select(x => x.Trim(punctuation));
return words.Contains(searchWord, StringComparer.OrdinalIgnoreCase);
}
But is throwing the same error - http 500
EDITED 2
Added ToList() - db.tblProducts.ToList().... In this case we retrieve all data from Data Base and filter them in memory. If we don't retrieve all data before filtering .Net tries to create request to SQL with filtration and can't because there are .Net methods as CheckWord().
I think we can get required data without retrieving all table into memory, but don't know how. As variant we should write specific Stored Procedure and use it. Get all into memory is a simplest way (but not faster)
Please, look at this post Get only Whole Words from a .Contains() statement
Actually, for your case solution can be:
IEnumerable<tblProduct> tblProduct = db.tblProducts.ToList()
.Where(x => Regex.Match(x.PrdKeyword, $#"\b{SearchText}\b", RegexOptions.IgnoreCase).Success)
.AsEnumerable();
Option 2. Without regexp:
public static bool CheckWord(string source, string searchWord)
{
if (source == null)
return false;
var punctuation = source.Where(Char.IsPunctuation).Distinct().ToArray();
var words = source.Split().Select(x => x.Trim(punctuation));
return words.Contains(searchWord, StringComparer.OrdinalIgnoreCase);
}
[HttpGet]
[Route("api/tblProducts/AllProductbySearch/{SearchText}")]
[ResponseType(typeof(IEnumerable<tblProduct>))]
public IHttpActionResult AllProductbySearch(string SearchText)
{
IEnumerable<tblProduct> tblProduct = db.tblProducts.ToList()
.Where(x => CheckWord(x.PrdKeyword, SearchText)).AsEnumerable();
if (tblProduct == null)
{
return NotFound();
}
return Ok(tblProduct);
}
Sorry, I'm from phone now, there can be mistakes here. Will try it in 3-4 hour
You are making a simple mistake. You just need to use .Equals instead of .Contains.
When you use Contains .Net will check if the input string is part of the main string. Whereas Equals will check for exact match.
var mainStr = “long string with Hello World”;
var inputStr = “Hello”;
var status = mainStr.Contains(inputStr);
// Value of status is `true`
status = mainStr.Equals(inputStr);
// Value of status is `false`
So your code should look like this:
IEnumerable<tblProduct> tblProduct = db.tblProducts.Where(x=>x.PrdKeyword.Equals(SearchText)).AsEnumerable();
.Equals can also help you find exact match with or without having case-sensitive check in force. The single-parameterised method does a Case-Sensitive check whereas the other overridden methods of .Equals gives you an opportunity to ignore it.
Hope this helps!
More a general question, but how can I write LINQ Lambda expressions such that they will return a default string or simply an empty string if the LINQ expression fails or returns nothing. In XSLT XPath if a match fails then one just got nothing, and the application did not crash whereas in LINQ one seems to get exceptions.
I use First() and have tried FirstOrDefault().
So example queries may be:
Customers.First(c=>c.id==CustId).Tasks.ToList();
or
Customers.Where(c=>c.id==CustId).ToList();
or
Model.myCustomers.Where(c=>c.id==CustId);
etc.
Whatever the query, if it returns no records or null, then is there a general approach to ensure the query fails gracefully?
Thanks.
There isn't anything elegant built into C# for propagating nulls when you access properties. You could create your own extension methods:
public static class Extensions
{
public static TValue SafeGet<TObject, TValue>(
this TObject obj,
Func<TObject, TValue> propertyAccessor)
{
return obj == null ? default(TValue) : propertyAccessor(obj);
}
public static IEnumerable<T> OrEmpty<T>(this IEnumerable<T> collection)
{
return collection ?? Enumerable.Empty<T>();
}
}
Used like this:
Customers.FirstOrDefault(c => c.id==CustId).SafeGet(c => c.Tasks).OrEmpty().ToList();
Customers.First(c=>c.id==CustId) will crash if there is no matching record.
There are few ways you can try to find it, if you use FirstOrDefault that'll return NULL if no match is found and you can check for NULL.
Or, you can use the .Any syntax which checks if you have any record and returns boolean.
The only query I would expect to throw an exception would be the first one (assuming that Customers is a valid collection and not null itself):
Customers.First(c=>c.id==CustId).Tasks.ToList();
This will throw an exception if there is no customer with an id of CustId (you have some casing issues with your property and variable names).
If you don't wish to throw an exception on no match, then use FirstOrDefault as you mention, and do a null check, e.g:
var customer = Customers.FirstOrDefault(c => c.id == CustId);
if (customer == null)
{
// deal with no match
return;
}
var taskList = customer.Tasks.ToList();
I have a Linq query which I am selecting into a string, of course a string can contain null!
So is there a way I can throw an exception within my Linq query, if I detect a null?
Can I decorate my class with an attribute that won't let it allow null?
I would like to wrap my Linq query in a try catch, and as soon as a null is detected then it would enter the catch, and I can handle it.
Edit
Here's my Linq query, it's quite simple currently. I am going to extend it, but this shows the basic shape:
var localText = from t in items select new Items { item = t.name }
Basically item is set to t.name, t.name is a string so it could be empty / null is this perfectly legal as its a string and strings can hold NULL.
So if it returns NULL then I need to throw an exception. Actually it would be handy to be able to throw an exception is NULL or empty.
I seemed to remember some kind of Attributes that can be set on top of properties that says "Don't accept null" etc.?
Edit
I think I found it: http://msdn.microsoft.com/en-us/library/system.componentmodel.dataannotations.requiredattribute.aspx
This doesn't allow null or strings so I presume it throws an exception, I have used this with MVC but I am not sure if I can use it with a standard class.
As a string being null isn't particularly exceptional, you could do something like:
var items = myStrings.Where(s => !string.IsNullOrEmpty(s)).Select(s => new Item(s));
UPDATE
If you are reading this data from an XML file, then you should look into LINQ to XML, and also use XSD to validate the XML file rather than throwing exceptions on elements or attributes that don't contain strings.
You could try intentionally generating a NullReferenceException:
try
{
//Doesn't change the output, but throws if that string is null.
myStrings.Select(s=>s.ToString());
}
catch(NullReferenceException ex)
{
...
}
You could also create an extension method you could tack on to a String that would throw if null:
public static void ThrowIfNull(this string s, Exception ex)
{
if(s == null) throw ex;
}
...
myString.ThrowIfNull(new NullReferenceException());
Why do you want to throw an exception in this case? This sounds like throwing the baby out with the bath water for something that should not happen in the first place.
If you just want to detect that there are null/empty items:
int nullCount= items.Count( x=> string.IsNullOrEmpty(x.name));
If you want to filter them out:
var localText = from t in items where !string.IsNullOrEmpty(t.name) select new Items { item = t.name };
I have a piece of code which combines an in-memory list with some data held in a database. This works just fine in my unit tests (using a mocked Linq2SqlRepository which uses List).
public IRepository<OrderItem> orderItems { get; set; }
private List<OrderHeld> _releasedOrders = null;
private List<OrderHeld> releasedOrders
{
get
{
if (_releasedOrders == null)
{
_releasedOrders = new List<nOrderHeld>();
}
return _releasedOrders;
}
}
.....
public int GetReleasedCount(OrderItem orderItem)
{
int? total =
(
from item in orderItems.All
join releasedOrder in releasedOrders
on item.OrderID equals releasedOrder.OrderID
where item.ProductID == orderItem.ProductID
select new
{
item.Quantity,
}
).Sum(x => (int?)x.Quantity);
return total.HasValue ? total.Value : 0;
}
I am getting an error I don't really understand when I run it against a database.
Exception information:
Exception type: System.NotSupportedException
Exception message: Local sequence cannot be used in LINQ to SQL
implementation of query operators
except the Contains() operator.
What am I doing wrong?
I'm guessing it's to do with the fact that orderItems is on the database and releasedItems is in memory.
EDIT
I have changed my code based on the answers given (thanks all)
public int GetReleasedCount(OrderItem orderItem)
{
var releasedOrderIDs = releasedOrders.Select(x => x.OrderID);
int? total =
(
from item in orderItems.All
where releasedOrderIDs.Contains(item.OrderID)
&& item.ProductID == orderItem.ProductID
select new
{
item.Quantity,
}
).Sum(x => (int?)x.Quantity);
return total.HasValue ? total.Value : 0;
}
I'm guessing it's to do with the fact
that orderItems is on the database
and releasedItems is in memory.
You are correct, you can't join a table to a List using LINQ.
Take a look at this link:
http://flatlinerdoa.spaces.live.com/Blog/cns!17124D03A9A052B0!455.entry
He suggests using the Contains() method but you'll have to play around with it to see if it will work for your needs.
It looks like you need to formulate the db query first, because it can't create the correct SQL representation of the expression tree for objects that are in memory. It might be down to the join, so is it possible to get a value from the in-memory query that can be used as a simple primitive? For example using Contains() as the error suggests.
You unit tests work because your comparing a memory list to a memory list.
For memory list to database, you will either need to use the memoryVariable.Contains(...) or make the db call first and return a list(), so you can compare memory list to memory list as before. The 2nd option would return too much data, so your forced down the Contains() route.
public int GetReleasedCount(OrderItem orderItem)
{
int? total =
(
from item in orderItems.All
where item.ProductID == orderItem.ProductID
&& releasedOrders.Contains(item.OrderID)
select new
{
item.Quantity,
}
).Sum(x => (int?)x.Quantity);
return total.HasValue ? total.Value : 0;
}
I'm using LINQ to SQL and C#. I have two LINQ classes: User and Network.
User has UserID (primary key) and NetworkID
Network has NetworkID (primary key) and an AdminID (a UserID)
The following code works fine:
user.Network.AdminID = 0;
db.SubmitChanges();
However, if I access the AdminID before making the change, the change never happens to the DB. So the following doesn't work:
if(user.Network.AdminID == user.UserID)
{
user.Network.AdminID = 0;
db.SubmitChanges();
}
It is making it into the if statement and calling submit changes. For some reason, the changes to AdminID never make it to the DB. No error thrown, the change just never 'takes'.
Any idea what could be causing this?
Thanks.
I just ran a quick test and it works fine for me.
I hate to ask this, but are you sure the if statement ever returns true? It could be you're just not hitting the code which changes the value.
Other than that we might need more info. What are the properties of that member? Have you traced into the set statement to ensure the value is getting set before calling SubmitChanges? Does the Linq entity have the new value after SubmitChanges? Or do both the database AND the Linq entity fail to take the new value?
In short, that code should work... so something else somewhere is probably wrong.
Here's the original post.
Here's a setter generated by the LinqToSql designer.
Code Snippet
{
Contact previousValue = this._Contact.Entity;
if (((previousValue != value)
|| (this._Contact.HasLoadedOrAssignedValue == false)))
{
this.SendPropertyChanging();
if ((previousValue != null))
{
this._Contact.Entity = null;
previousValue.ContactEvents.Remove(this);
}
this._Contact.Entity = value;
if ((value != null))
{
value.ContactEvents.Add(this);
this._ContactID = value.ID;
}
else
{
this._ContactID = default(int);
}
this.SendPropertyChanged("Contact");
}
}
This line sets the child's property to the parent.
this._Contact.Entity = value;
This line adds the child to the parent's collection
value.ContactEvents.Add(this);
The setter for the ID does not have this second line.
So, with the autogenerated entities...
This code produces an unexpected behavior:
myContactEvent.ContactID = myContact.ID;
This code is good:
myContactEvent.Contact = myContact;
This code is also good:
myContact.ContactEvents.Add(myContactEvent);
I had this issue. The reason was one dumb line of code:
DBDataContext db { get { return new DBDataContext(); } }
obviously it should be:
DBDataContext db = new DBDataContext();