I have a dictionary:
Dictionary<string, long> Reps = new Dictionary<string, long>();
and I want to update the values while iterating through all items, like this:
foreach (string key in Reps.keys)
{
Reps[key] = 0;
}
it is giving me an error saying:
"Collection was modified; enumeration operation may not execute"
can anyone tell me why it is giving me this error, because I have one more function that adds the value, and it is called when button is clicked:
public static void Increment(string RepId, int amount)
{
long _value = Convert.ToInt64(Reps[RepId]);
_value = _value + amount;
Reps[RepId] = _value;
}
and this function is working fine. so whats the problem when updating all the values? And whats the solution for this?
more simplified, do this:
foreach (string key in Reps.keys.ToList())
{
Reps[key] = 0;
}
and the reason for the error is you are trying to edit the actual object which is in use and if you make a copy of it and then use it like this:
var repscopy = Reps;
foreach (string key in repscopy.keys)
{
Reps[key] = 0;
}
it'll give the same error as it also pointing to the original object, and when the ToList() is added it created a new object of List
The problem is no updating the values, you just cannot change the collection that your foreach() is based on while the foreach is being iterated.
Try somehting like this
List<string> keylist = Reps.keys.ToList();
foreach(string r in keylist)
{
Reps[r] = 0;
}
this would work.
This happens because you are changing the element in the Dictionary<string, long> while looping over it with foreach. Try this.
foreach (string key in Reps.Keys.ToList())
{
Reps[key] = 0;
}
Now you are looping over a list created from the dictionarys key. As it is not the original collection thats modified, the error will go away.
Related
Just started learning Dapper. I have an ADO.NET background. Using a demo I downloaded, I can insert/delete data from a webform into a MySql table just fine. This, however, I have searched all morning on.
In retrieving a single row from the db by ID, it doesn't return a LIST<>, it seems to be just an object (using code from the demo I downloaded). The query works, I get the object back. It has the fields: "ProductID, Description and Price".
The only way I could get the values to those three fields was like this:
System.Reflection.PropertyInfo pi = Product.GetType().GetProperty("ProductID");
System.Reflection.PropertyInfo desc = Product.GetType().GetProperty("Description");
System.Reflection.PropertyInfo price = Product.GetType().GetProperty("Price");
int _ProductID = (int)(pi.GetValue(Product, null));
string _Description = (string)(desc.GetValue(Product, null));
decimal _Price = (decimal)(price.GetValue(Product, null));
This works and gets the correct values for the three fields.
I'm used to looping through DataTables, but I just think there is probably a better way to get those values.
Is this the correct way to do this or am I missing something? I did actually read documentation and mess with this all morning before asking, too.
Some of the things I looked at seem to be very complex. I thought Dapper was supposed to simplify things.
OK, Thanks Marc. It was difficult for me to see what was supposed to be in the Dapper class files and what was supposed to be in my code behind. The original demo way of getting a product by ID had the query as .FirstOrDefault();
I changed everything to return a List<> and it all worked. I'm sure my ADO.NET is showing, but this works. In Dapper class files:
public List<Product> ProductAsList(int Id)
{
return this._db.Query<Product>("SELECT * FROM Cart_product WHERE ProductID=#Id", new { Id = Id }).**ToList()**;
}
This is just getting one row that matched the ProductID.
In page codebehind:
protected void CartItemAdd(string ProductId) // passing it the selected ProductID
{
var results = cartservice.ProductAsList(Convert.ToInt32(ProductId));
// returns that one row using Dapper ProductAsList(ProductId)
int _ProductId = 0;
string Description = string.Empty;
decimal Price = 0;
// Loop through the list and get the value of each item:
foreach (Product obj in results)
{
_ProductId = obj.ProductID;
Description = obj.Description;
Price = obj.Price;
}
// Using Dapper to insert the selected product into the shopping cart (table):
String UserName = "jbanks";
cartitem = new CartItem();
cartitem.ProductID = _ProductId;
cartitem.Quantity = 1;
cartitem.Description = Description;
cartitem.Price = Price;
cartitem.Created = DateTime.Now;
cartitem.CreatedBy = UserName;
result = cartservice.AddCartItem(cartitem);
if (result)
{
lblMessage.Text = string.Empty;
lblMessage.Text = "Successfully added a cart item";
}
}
}
It does indeed look up the product from one table and insert a selected item into another table.
Thanks again!
The main Query<T> API returns an IEnumerable<T>, which often will be a List<T>; the AsList<T>() extension method can get it back to a list without a copy, but either way: they are just T, for whatever T you asked for. If you asked for Query<Product>, then: they should be Product instances:
var results = connection.Query<Product>(someSql, someArgs); // perhaps .AsList()
foreach (Product obj in results) { // "var obj" would be fine here too
// now just use obj.ProductID, obj.Description and obj.Price
}
If that didn't work: check that you used the <T> version of Query. There is a non-generic variant too, which returns dynamic. Frankly, you should almost always use the <T> version.
Note: I'm assuming that somewhere you have something like
class Product {
public int ProductID {get;set;}
public string Description {get;set;}
public decimal Price {get;set;}
}
After reading this article:
http://blogs.msdn.com/b/tilovell/archive/2009/12/29/the-trouble-with-system-activities-foreach-and-parallelforeach.aspx
I have defined the ForEachFactory as follows:
public class ForEachFactory<T> : IActivityTemplateFactory
{
public Activity Create(DependencyObject target)
{
return new ForEach<T>
{
DisplayName = "ForEachFromFactory",
Body = new ActivityAction<T>
{
Argument = new DelegateInArgument<T>("item")
}
};
}
}
All works well but is it possible to check how that DelegeateInArgument in my case named "item" changes its value ?
So if i have defined an array in the variables section and initialized with
{1, 2, 3} i need a way to check how the "item" takes value 1, 2 and then 3.
To be more accurate, i've added this pic, with a breakpoint on the WriteLine activity inside the foreach. When the execution will stop there, is there a way to find out what the value of item is ?
EDIT 1:
Possible solution in my case:
After struggling a bit more i found one interesting thing:
Adding one of my custom activities in the Body of the ForEach, i am able to get the value of the item like this :
So, my activity derives from : CodeActivity
Inside the protected override String[] Execute(CodeActivityContext context) i am doing this job.To be honest, this solves the thing somehow, but it is doable only in my custom activities. If i would put a WriteLine there for example, i would not be able to retrieve that value.
you can access the DelegeateInArgument of a ForEach activity by inspecting the ModelItem trees parent and checking for DelegeateInArgument's. If you need a specific code example to achieve this I may need a some time to code the example. As it has been a long time since I did this, see my question i asked over on msdn
So basically where your break point is, you can access the variable values as these are defined with n the scope of your activity as 'variables'. However the 'item' variable is actually only accessible from the parent loop activity. So you have to get the model item of the current executing activity and then traverse up the tree to find the parent containing the desired DelegateInArgument.
Can you flesh out exactly what you want to achieve? Is it that when your debugging the workflow in the re-hosted designer you want to display the variable values to the user as they change in the UI?
Edit - added tracking example
So as your wanting to display the variable values during execution of the workflow we need to use tracking to achieve this. In the example your using the author has already implemented some basic tracking. So to achieve the extended variable tracking you want you will need to alter the tracking profile.
Firstly amend the WorkflowDesignerHost.xaml.cs file alter the RunWorkflow method to define the SimulatorTrackingParticipant as below.
SimulatorTrackingParticipant simTracker = new SimulatorTrackingParticipant()
{
TrackingProfile = new TrackingProfile()
{
Name = "CustomTrackingProfile",
Queries =
{
new CustomTrackingQuery()
{
Name = all,
ActivityName = all
},
new WorkflowInstanceQuery()
{
**States = {all },**
},
new ActivityStateQuery()
{
// Subscribe for track records from all activities for all states
ActivityName = all,
States = { all },
**Arguments = {all},**
// Extract workflow variables and arguments as a part of the activity tracking record
// VariableName = "*" allows for extraction of all variables in the scope
// of the activity
Variables =
{
{ all }
}
}
}
}
};
This will now correctly capture all workflow instance states rather than just Started/Completed. You will also capture all Arguments on each activity that records tracking data rather than just the variables. This is important because the 'variable' were interested in is actually (as discussed earlier) a DelegateInArgument.
So once we have changed the tracking profile we also need to change the SimulatorTrackingParticipant.cs to extract the additional data we are now tracking.
If you change the OnTrackingRecordReceived method to include the following sections these will capture variable data and also Argument data during execution.
protected void OnTrackingRecordReceived(TrackingRecord record, TimeSpan timeout)
{
System.Diagnostics.Debug.WriteLine(
String.Format("Tracking Record Received: {0} with timeout: {1} seconds.", record, timeout.TotalSeconds)
);
if (TrackingRecordReceived != null)
{
ActivityStateRecord activityStateRecord = record as ActivityStateRecord;
if (activityStateRecord != null)
{
IDictionary<string, object> variables = activityStateRecord.Variables;
StringBuilder vars = new StringBuilder();
if (variables.Count > 0)
{
vars.AppendLine("\n\tVariables:");
foreach (KeyValuePair<string, object> variable in variables)
{
vars.AppendLine(String.Format(
"\t\tName: {0} Value: {1}", variable.Key, variable.Value));
}
}
}
if (activityStateRecord != null)
{
IDictionary<string, object> arguments = activityStateRecord.Arguments;
StringBuilder args = new StringBuilder();
if (arguments.Count > 0)
{
args.AppendLine("\n\tArgument:");
foreach (KeyValuePair<string, object> argument in arguments)
{
args.AppendLine(String.Format(
"\t\tName: {0} Value: {1}", argument.Key, argument.Value));
}
}
//bubble up the args to the UI for the user to see!
}
if((activityStateRecord != null) && (!activityStateRecord.Activity.TypeName.Contains("System.Activities.Expressions")))
{
if (ActivityIdToWorkflowElementMap.ContainsKey(activityStateRecord.Activity.Id))
{
TrackingRecordReceived(this, new TrackingEventArgs(
record,
timeout,
ActivityIdToWorkflowElementMap[activityStateRecord.Activity.Id]
)
);
}
}
else
{
TrackingRecordReceived(this, new TrackingEventArgs(record, timeout,null));
}
}
}
Hope this helps!
asp.net C#4
I have a simple class to working with query strings.
A new instance is created like this:
public QueryString(string querystring)
{
try
{
_table = new Hashtable();
if (querystring.Length > 0)
{
foreach (string pair in querystring.Split('&'))
{
string[] item = pair.Split('=');
_table.Add(item[0].ToLower(), item[1]);
}
}
}
catch (Exception)
{
}
}
I want to add a method to this that will remove a key value pair. I don't want it to return a new querystring, I just want it to remove the pair from the current instance. Not sure how to do that since it says I can't assign a value to 'this'
public void Remove(string key)
{
String querystring = this.ToString();
try
{
_table = new Hashtable();
if (key.Length > 0)
{
foreach (string pair in querystring.Split('&'))
{
string[] item = pair.Split('=');
if (item[0] != key)
{
_table.Add(item[0].ToLower(), item[1]);
}
}
this = _table;
}
}
catch (Exception)
{
}
}
You're overcomplicating things. Since your class's state is made up of the _table field, all you need to do is remove the item with the given key from that field.
The following example replaces your untyped Hashtable wit a strongly-typed Dictionary. I also chose to initialize the dictionary with a LINQ statement, but you could keep your old code there if you prefer.
public class QueryString
{
private readonly Dictionary<string, string> _table;
public QueryString(string querystring)
{
if (querystring.Length > 0)
{
var pairs =
from pair in querystring.Split('&')
let item = pair.Split('=')
select new {key = item[0], value = item[1]};
_table = pairs.ToDictionary(p => p.key, p => p.value);
}
}
public void Remove(string key)
{
_table.Remove(key);
}
}
You cannot assign a value to this since it is a reference to the object itself.
However, if you remove the line this = _table; , isn't things working as they should then? I guess your ToString() is somewhat using the hashtable to generate a "printer friendly" QueryString, and if that is the case, the way I see it, your Remove() method should be working (since you are replacing the _table variable with a new HashTable not including the key-value pair you want to exclude).
you are passing a querystring into the class so the original querystring IS intact.
However you then break down the querystring into a a Hashtable of key/value pairs. If you want to keep THAT intact you need to clone the HashTable and perform the remove on the clone.
In any case it's probably a good idea to keep the querystring you are passing in as a constructor parameter in a member variable for safe keeping.
{
--
public static IEnumerable<Datarow> Codes(string topvalue)
{
DataTable itemCodes = new DataTable();
itemCodes.Columns.Add("itemId");
itemCodes.Columns.Add("itemCode");
itemCodes.Rows.Add(0, firstCallingCode);
DataTable Codes = GetAllItems().Tables[0];
foreach (DataRow item in Codes.Rows)
{
if (item["ItemCode"] != DBNull.Value)
{
itemCodes.Rows.Add(item.Field<int?>("itemId"), item.Field<string>("itemCode"));
}
}
return itemCodes.AsEnumerable();d
}
how can i bind it to dropdownlist: i tried this
ddcodes.datasource = codes.getenumerable();
ddcodes.databind();
when i do this i get error about typecast. i can not solve it tried a lot please help.
my method is actually this
public static IEnumerable"Datarow" Codes(string topvalue)
dont know why editor took that datarow off. bracket and datarow.
You just need to pass in the return value from the Codes method.
ddcodes.datasource = Codes();
ddcodes.databind();
You don't need to "get" an enumerable. The Codes method is already returning one.
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