This method I am using to fill the data source for a grid view, but for when getnew is false, it won't return any value , just returns a list with a single null value in it.
private List<T> GetAll_T(bool getNew)
{
if (getNew)
return (ViewState["T"] = Get_T()) as List<T>;
//Get_T() returns a CustomList
return new List<T>
{
ViewState["T"] != null ?
ViewState["T"] as T:
(T)(ViewState["T"] = Get_T()) Collection
};
}
it gives me a warning for second line[when view state is null].expression is always false
why there is warning, when it's logically correct !
It is not clear from your code snippet what CustomerService.GetAllCustomer() returns.
You use it both like it returns a list on line(2) of the function and like it returns a single object on line(8).
I suggest writing it like this
private List<CustomerMaster> GetAllCustomer(bool getNew)
{
if (getNew || null == ViewState["CustomerDataset"])
ViewState["CustomerDataset"] = CustomerService.GetAllCustomer();
return ViewState["CustomerDataset"] as List<CustomerMaster>;
}
Related
Currently I am querying a web service that returns a JSON string.
url = #"redacted url;
returnValue = new WebClient().DownloadString(url);
I am putting the return results into a list of items defined in a model class. I am then running a second JSON call searching a different field with that same search term.
url2 = #"redacted url2;
returnValue2 = new WebClient().DownloadString(url2);
I then create my lists and combine the lists using AddRange.
List<Order> shipments = JsonConvert.DeserializeObject<List<Order>>(returnValue);
List<Order> shipments2 = JsonConvert.DeserializeObject<List<Order>>(returnValue2);
shipments.AddRange(shipments2);
As a result there are some duplicates. To try and only return unique records I am using the command Distinct when sending to my MVC view from the controller.
return View(shipments.OrderBy(x => x.dtDateReceived).Distinct().ToList());
But for some reason it's still returning duplicates.
Any ideas on what I am doing wrong here?
Thanks in advance for any help!
I ended up correcting it using Shyju's comment above.
I changed the Distinct to the following.
return View(shipments.OrderBy(x => x.dtDateReceived).Distinct(new OrderComparer()).ToList());
Then built the following compare functions
// Custom comparer for the Order class
class OrderComparer : IEqualityComparer<Order>
{
// Orders are equal if their names and order numbers are equal.
public bool Equals(Order x, Order y)
{
//Check whether the compared objects reference the same data.
if (Object.ReferenceEquals(x, y)) return true;
//Check whether any of the compared objects is null.
if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null))
return false;
//Check whether the order's properties are equal.
return x.sWorkOrderNumber == y.sWorkOrderNumber && x.sCustomerOrderName == y.sCustomerOrderName;
}
// If Equals() returns true for a pair of objects
// then GetHashCode() must return the same value for these objects.
public int GetHashCode(Order order)
{
//Check whether the object is null
if (Object.ReferenceEquals(order, null)) return 0;
//Get hash code for the sCustomerOrderName field if it is not null.
int hashOrderName = order.sCustomerOrderName == null ? 0 : order.sCustomerOrderName.GetHashCode();
//Get hash code for the sWorkOrderNumber field.
int hashOrderCode = order.sWorkOrderNumber.GetHashCode();
//Calculate the hash code for the order.
return hashOrderName ^ hashOrderCode;
}
}
I have a Category entity which has a Nullable ParentId field. When the method below is executing and the categoryId is null, the result seems null however there are categories which has null ParentId value.
What is the problem in here, what am I missing?
public IEnumerable<ICategory> GetSubCategories(long? categoryId)
{
var subCategories = this.Repository.Categories.Where(c => c.ParentId == categoryId)
.ToList().Cast<ICategory>();
return subCategories;
}
By the way, when I change the condition to (c.ParentId == null), result seems normal.
Other way:
Where object.Equals(c.ParentId, categoryId)
or
Where (categoryId == null ? c.ParentId == null : c.ParentId == categoryId)
The first thing to do is to put on logging, to see what TSQL was generated; for example:
ctx.Log = Console.Out;
LINQ-to-SQL seems to treat nulls a little inconsistently (depending on literal vs value):
using(var ctx = new DataClasses2DataContext())
{
ctx.Log = Console.Out;
int? mgr = (int?)null; // redundant int? for comparison...
// 23 rows:
var bosses1 = ctx.Employees.Where(x => x.ReportsTo == (int?)null).ToList();
// 0 rows:
var bosses2 = ctx.Employees.Where(x => x.ReportsTo == mgr).ToList();
}
So all I can suggest is use the top form with nulls!
i.e.
Expression<Func<Category,bool>> predicate;
if(categoryId == null) {
predicate = c=>c.ParentId == null;
} else {
predicate = c=>c.ParentId == categoryId;
}
var subCategories = this.Repository.Categories
.Where(predicate).ToList().Cast<ICategory>();
Update - I got it working "properly" using a custom Expression:
static void Main()
{
ShowEmps(29); // 4 rows
ShowEmps(null); // 23 rows
}
static void ShowEmps(int? manager)
{
using (var ctx = new DataClasses2DataContext())
{
ctx.Log = Console.Out;
var emps = ctx.Employees.Where(x => x.ReportsTo, manager).ToList();
Console.WriteLine(emps.Count);
}
}
static IQueryable<T> Where<T, TValue>(
this IQueryable<T> source,
Expression<Func<T, TValue?>> selector,
TValue? value) where TValue : struct
{
var param = Expression.Parameter(typeof (T), "x");
var member = Expression.Invoke(selector, param);
var body = Expression.Equal(
member, Expression.Constant(value, typeof (TValue?)));
var lambda = Expression.Lambda<Func<T,bool>>(body, param);
return source.Where(lambda);
}
My guess is that it's due to a rather common attribute of DBMS's - Just because two things are both null does not mean they are equal.
To elaborate a bit, try executing these two queries:
SELECT * FROM TABLE WHERE field = NULL
SELECT * FROM TABLE WHERE field IS NULL
The reason for the "IS NULL" construct is that in the DBMS world, NULL != NULL since the meaning of NULL is that the value is undefined. Since NULL means undefined, you can't say that two null values are equal, since by definition you don't know what they are.
When you explicitly check for "field == NULL", LINQ probably converts that to "field IS NULL". But when you use a variable, I'm guessing that LINQ doesn't automatically do that conversion.
Here's an MSDN forum post with more info about this issue.
Looks like a good "cheat" is to change your lambda to look like this:
c => c.ParentId.Equals(categoryId)
You need to use operator Equals:
var subCategories = this.Repository.Categories.Where(c => c.ParentId.Equals(categoryId))
.ToList().Cast<ICategory>();
Equals fot nullable types returns true if:
The HasValue property is false, and the other parameter is null. That is, two null values are equal by definition.
The HasValue property is true, and the value returned by the Value property is equal to the other parameter.
and returns false if:
The HasValue property for the current Nullable structure is true, and the other parameter is null.
The HasValue property for the current Nullable structure is false, and the other parameter is not null.
The HasValue property for the current Nullable structure is true, and the value returned by the Value property is not equal to the other parameter.
More info here Nullable<.T>.Equals Method
Or you can simply use this. It will also translate to a nicer sql query
Where((!categoryId.hasValue && !c.ParentId.HasValue) || c.ParentId == categoryId)
What about something simpler like this?
public IEnumerable<ICategory> GetSubCategories(long? categoryId)
{
var subCategories = this.Repository.Categories.Where(c => (!categoryId.HasValue && c.ParentId == null) || c.ParentId == categoryId)
.ToList().Cast<ICategory>();
return subCategories;
}
Linq to Entities supports Null Coelescing (??) so just convert the null on the fly to a default value.
Where(c => c.ParentId == categoryId ?? 0)
I have a list and setting the list to the exact item that is in it's dataProvider would not select it programmatically. Here is the code:
if (list.selectedItem != iDocument) {
var length:int = documentsCollection.length;
for (var i:int;i<length;i++) {
jDocument = IDocumentData(documentsCollection.getItemAt(i));
if (jDocument.uid==iDocument.uid) {
list.selectedItem = IDocumentData(documentsCollection.getItemAt(i));
break;
}
}
}
There were two issues.
I had applied a sort to the ArrayCollection and the field was not in the item. I had copied code from another project and the field was "#name" since it was an XMLListCollection. The sort field should have been set to "name".
So when you set the selectedItem property it looks in the collection and if the collection has a sort then it looks in the findItem() call which does a compare function that checks if the item has the field name in the item. If not it throws an error. Since I had the incorrect field name an error was thrown. If an error is thrown then the pursuit to find the selected item is abandoned and selected index is -1.
Code from ListCollectionView.as:
try
{
return sort.findItem(localIndex, values, mode, insertIndex);
}
catch (e:SortError)
{
// usually because the find critieria is not compatible with the sort.
}
return -1;
Code from Sort.as:
var hasFieldName:Boolean;
try
{
hasFieldName = values[fieldName] !== undefined;
}
catch(e:Error)
{
hasFieldName = false;
}
if (hasFieldName)
{
if (!hadPreviousFieldName)
{
message = resourceManager.getString(
"collections", "findCondition", [ fieldName ]);
throw new SortError(message);
}
else
{
fieldsForCompare.push(fieldName);
}
}
The second issue was that the List uses an exact equality operator so it uses "===" instead of "==". This means that you have to make sure you are passing in the exact instance of the item in the list.
I'm seeing something weird in my actionscript code
I have two classes foo and bar, bar extends foo. In a model class I have a foo member variable, I assign an bar object to the foo variable. But after the assignment the foo variable is null.
[Bindable] public var f:foo;
public function someFunc(arr:ArrayCollection):void {
if(arr.length > 0) {
var tempBar:bar = arr.getItemAt(0) as bar;
if(tempBar != null) {
tempBar.someProp++;
f = tempBar;
// f is now null
}
}
}
Any ideas on what I could be doing wrong?
EDIT
Here is the exact code:
[Bindable] public var selectedCustomerJob:IDSCustomer;
public function selectedJobByIdCallback(evt:Event):void
{
var temp:IDSDTOArrayCollection = evt.currentTarget as IDSDTOArrayCollection;
if(null != temp && temp.length > 0)
{
selectedCustomerJob = IDSJob(temp.getItemAt(0));;
trace(" selectedCustomerJob: " + flash.utils.getQualifiedClassName(selectedCustomerJob));
trace(" jobToSelect type: " + flash.utils.getQualifiedClassName(temp.getItemAt(0)));
trace("jobToSelect super class: " + flash.utils.getQualifiedSuperclassName(temp.getItemAt(0)));
}
}
this is the trace output:
selectedCustomerJob: null
jobToSelect type: com.intuit.sb.cdm.v2::IDSJob
jobToSelect super class: com.intuit.sb.cdm.v2::IDSCustomer
Casting using the as keyword returns null when it fails. In this case, the first item in the array collection may not be an object of type Bar as you expect; it could be a Foo or something else. You can cast subclass object to base-class but not the other way.
Use the parenthesis syntax for casting - it'll throw an exception if cast fails and thus you can figure out the type of arr.getItemAt(0).
//Change
var tempBar:Bar = arr.getItemAt(0) as Bar;
//to
var tempBar:Bar = Bar(arr.getItemAt(0));
to make sure that the first item in the array collection is indeed a Bar instance (and not Foo or something else).
Otherwise you can find the type using
trace(flash.utils.getQualifiedClassName(arr.getItemAt(0)));
if(tempBar != null) {
tempBar.someProp++;
f = tempBar;
// f is now null
}
By the way, I believe the posted code is not the exact code you ran because for f to be null, tempBar should be null as you assigning it to f. In that case the code inside if should not be executed as you're checking for null inside if. Even if it enters the if block, it will throw a null pointer error (#1009) in the first line where you're trying to increment tempBar.someProp
Im trying to extend the flex ArrayCollection to be able to search for an object containing specific data and give it back.
Here is my function:
public function getItemContaining(value: String): Object {
//Loop through the collection
for each(var i: Object in this) {
//Loop through fields
for(var j: String in i) {
//If field value is equal to input value
if(i[j] == value) {
return i;
}
}
}
//If not found
return null;
}
Problem is j is always null so the second loop never works. So I read flex loop descriptions and actually it should work just fine. What can possibly be the problem?
Try it like this:
for (var name:String in myObject){
trace(name + ":" + myObject[name];
}
Okay that was actually the same you were doing. The error must be in this line:
for each(var i: Object in this) {
Try using this:
for each(var i: Object in this.source) {
My first instinct would be to have a look at data type. You're setting up a loop declaring j:String and the symptom is that j is always null. This suggests to me that Flex is failing to interpret the elements of i as strings. If Flex only recognizes the elements of i as Objects (because all Strings are Objects, and Objects are the lowest common denominator), it would return null for j:String.
Try this for your inner loop:
for(var j: Object in i) {
//If field value is equal to input value
if(i[j] is String && (i[j] as String) == value) {
return i;
}
}
if you are using ArrayCollection as your datasource, you should look at using the IViewCursor interface. You can supply a custom compare function, or supply the fields top compare to. This interface is well documented with examples in adobe/livedocs
var _cursor:IViewCursor;
var _idSortField:SortField;
var _idSort:Sort = new Sort();
_idSortField = new SortField();
_idSortField.compareFunction = this.myCompareFunction;
_idSort.fields = [_idSortField];
myArrayCollection.sort = _idSort;
myArrayCollection.refresh();
_cursor = myArrayCollection.createCursor();
if (_cursor.findAny(search))
return _cursor;
if you are search for a value in a specific property, then its even easier. Here's the link to adobe livedocs on this topic