DataSet is said to be a collection of one or more DataTable objects.
Is it possible to use an array of DataTable objects?
If yes, then why use a DataSet? Are there any advantages?
Please help!
A DataSet has some extra properties rather than a simple Array of DataTable. For instance, it is serializable.
You should always stick to existing .NET classes rather than inventing new ones.
In an object oriented language, people preferred to use an object rather than an array. It's more intuitive for anyone reading your code if you use DataSet.Datatable(TheTableName). You can briefly describe what's inside of that table with the table name. By contrast, creating an array of tables is not a good idea. Take a look at this code: DataTableArray(0) = MyDataTable . The next time if you tried to find MyDataTable, it's not possible for anyone who's reading your code to remember that MyDataTable is restored in DataTableArray with an index of 0. This concept is also applied in the concept of LINQ.
Please take a look at this page. MSDN helps.
https://msdn.microsoft.com/zh-tw/library/bb397897.aspx
Related
I'm looking for a way to create dynamic input fields in Meteor.js. I've chosen not to use Aldeed's Autoform for greater control over the code. From front end point of view I have no issues to add dynamic fields with +/- button to add and remove fields. What I'm struggling with is the insert statement on the back end. How can one add dynamic insert in Meteor.js? Cheers!
Essentially you need a reactive array of element that's rendered to the DOM via {{#each}} ... {{/each}}. When the array changes the DOM would re-render.
There's no need to create your own reactive array, there's one here with an example that does exactmy what you're asking for:
http://reactivearray.meteor.com/
However I'd recommend going one step further and using the ViewModel package for this (by the same author). Here's an example which shows how to use it to insert fields:
http://viewmodel.meteor.com/#contacts
Tim
Thanks Tim, these are both pretty useful. I'm using Collection 2 so decided to use objects ('object.$'). This is easy solution for me. cheers.
I have a problem with the AdvancedDataGrid widget. When the dataProvider is an ArrayCollection (of arrays), the nth array (within the collection) is also the nth row within the grid, and I can jump and display the i-th row by scripting
adg.selectedIndex = i;
adg.scrollToIndex(i);
now, when I add a Grouping, the dataProvider ends up being a GroupingCollection2, and now the index in the dataprovider's source does not correspond to the index in the adg anymore (which is understandable, because it's being grouped).
How can I select and display a row in grouped data efficiently? Currently, I have to traverse the adg and compare each found item with its data attributes in order to find the correct index of the row within the adg, and jump to it like above. This process is very slow. Any thoughts?
edited later:
We already used a caching object as Shaun suggests, but it still didn't compensate for the search times. In order to fully construct a sorting of a list of things (which this problem equates to, as the list is completely reordered by the grouping), you always have to know the entire set. In the end we didn't solve that problem. The project is over now. I will accept Shaun's answer if no one knows a better way in three days.
Depending on what values your comparing against you can store the objects in a dictionary with the lookup using the property/properties that would be searched for, this way you have a constant time look-up for the object (no need to look at every single item). Say for example your using a property called id on an object then you can create an AS object like
var idLookup:Object = {};
for(myObject in objects)
idLookup[myObject.id] = myObject;
//Say you want multiple properties
//idLookup[myObject.id]={};
//idLookup[myObject.id][myObject.otherProp] = myObject;
now say the user types in an id you go into the idLookup object at that id property and retrieve the object:
var myObject:Object = idLookup[userInput.text];
myAdg.expandItem(myObject, true);
now when you want to get an object by id you can just do
http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/mx/controls/AdvancedDataGrid.html#expandItem()
I haven't done any thorough testing of this directly, but use a similar concept for doing quick look-ups for advanced filtering. Let me know if this helps at all or is going in the wrong direction. Also if you could clarify a bit more in terms of what types/number of values you need to lookup and if there's the possibility for multiple matches etc. I may be able to provide a better answer.
Good luck,
Shaun
I have been tasked with sifting through the worst classic asp spaghetti i've ever come across.
The script runs a series of recordsets in sequence, getting 1 record at a time. As the record is built it takes the id and passes it to the next loop, which gets data, and passes on the id to the next loop. It then continues in this manner and builds an unordered list, kicking out the required html as it goes.
Here are my efforts so far:
have a class delivering data via sqldatareaders and output these to nested repeaters (this failed due to not being able to loop and get the id)
Have a datatable populated with all the required data, then datatable.select to filter it out.
have 4 datareaders looping and building the ul arraylists (I
couldnt get the id's to match up)
Please can you suggest the best method
Yes of course it can be rewritten in ASP.NET - note that i said rewritten, not just refactored, there is no saving that code (which is okay for what it does, but things are different with ASP.NET).
To be honest, i didn't even check the code, it hurt my eyes. A lot. But in general you can use a nice SQLConnection object, and a SQLCommand, call a stored procedure and get a nice SqlDataReader full of data from which you can build a DataTable or an IEnumerable list of data objects. You then have a repeater type control (ListView, GridView etc) in the UI, simply by binding your datatable or list to that control will render the results.
With the ListView, you specify a template for each data item that is rendered. For a GridView you specify the columns (or column templates) and which properties on each data item the columns should bind to.
When you retrieve the data, you can leave it as a DataTable, or translate it into something else like a list (or array) of data objects. As long as your list/array implements IEnumerable you should be able to just assign the list to the ItemsSource property of the aforementioned repeater control and it will perform its magic.
You don't even have to use a SQLCommand and DataTable object - you could even use Linq to SQL and bind the results straight to your repeater control.
This is just a high level overview of how you could do it, there are a couple of different ways. Once done, your code is going to be way cleaner and more maintainable than the classic ASP code.
Edit: your main issue is how to produce an ordered list, which is what the current code is doing with its nested loops supplying IDs for the detail items.
I would suggest you take a step back, and rethink the sql. In fact, throw the current sql away, it is incredibly inefficient with the tools you have today. It takes literally tenths of a second, and just one database call to return a flat table of data. Your first instinct may be "but i don't want to return too much data!" - relax, even returning several thousand data rows can be a sub 1 second operation if done correctly. You can also restrict the returned data by passing parameters in to the stored proc, or appending them to the dynamic sql statement that you construct (although it pains me hugely to mention dynamic sql, i think it is evil, but some people still use it - i would not recommend it unless it was your only option). To sum up what i am saying, how your data is returned from the database and how it looks on screen are two different things, don't let one guide the other. You can get the data from the database, then manipulate it before rendering it to the UI.
If you still want to show the data as an ordered list, then use a ListView, define a template for each data item, then you can use LINQ to group or filter the data you like (the data item template can contain whatever HTML or ASP.NET controls you like, and that template gets rendered for each data item in the list of data). Alternatively, you could use a GridView, and then use the grouping capability of the GridView to do the work for you - just specify which column(s) you want to group on, and the GridView takes care of the rendering.
I have a relatively simple Listview that suddenly needs (due to new requirements) to have it's 'layout' extracted to a DataTable so that a common routine can convert it to an Excel spreadsheet for export purposes.
The ItemTemplate is just a series of Table Rows with some text, data-bound labels and textboxes with validators in the cells.
Usually, when trying to pull out a particular value (like what was entered into a text box), I use the ListViewItem's .FindControl method.
For Each objItem As ListViewItem In lvwOptions.Items
Dim objTextHrsLabor As TextBox = CType(objItem.FindControl("txtHrsOptByLabor"), TextBox)
decHours = CDec(objTextHrsLabor.Text)
Next
In this case, however, I'm trying to take all the data displayed - all the 'rows and columns' of the table that was created.
Inside the ForEach / Next loop of ListViewItems, I started a ForEach/Next loop of Controls for each instance's controls but I got some really strange results returned (like controls that had a couple of table cells in them).
I get the sense I'm headed in the wrong direction. All I want is for the nicely-formatted 5-line, 6 column table to be converted to a 5-line, 6-column data table.
Is there another avenue I should be looking at?
I would look at the underlying data source for your ListView.
The data source must be a collection or an IEnumerable and you should be able to iterate through it to build your data table.
If you know that all elements are of the same type then you can use the first element and look at its properties using reflection to determine which columns your table should contain. Then you can add DataRows to your table and fill in the columns using the property names.
This will probably be faster than iterating through the generated html of the ListView.
I used this approach for exporting a ListView to Excel: http://aspalliance.com/771_CodeSnip_Exporting_GridView_to_Excel.
I know it deals with a GridView, but I adapted it to a ListView (as long as the underlying structure is a table) and it worked fine for me.
HTH.
you can use..
listView1.Items[0].SubItems[0].Text
this will be helpful , really simple and easy . You can extract info right on the basis of index & use anyway you want.
Should be easy but google couldn't give me a straight answer. I have an array. The fields in the array have underscores that I would like to remove e.g. "Column_1" to "Column 1". Does anyone know a good way to do this without looping through the whole array and rebuilding it anew? I didn't see any methods in the reference that would make this easy. thx
Depending on where you are using this Array, you could use the labelFunction to format the data before presenting it. It is present in Lists, DataGrids and Trees.
But you'd only need this if you have a very large data and wouldn't want to loop over all the records before showing them. A labelFunction would "reprocess" the label everytime before it's presented.
Flex 3 has built in refactoring
Edit... I may have misunderstood..
If you want to format the data in the array just loop through it and use regex to remove the underscores... or you can modify your query which grabs the data (if it is populated from a query)