|
Is there a good reason to use a SqlDataReader for filling a DataTable into a DataSet instead of using a SqlDataAdapter?
|
|
|
|
|
Hi Dewald,
Not sure if you have found a solution to this as yet but this is what I do when I want to populate a comboBox from a db.
try
{
conn.Open();
string sql = @"select Titles, TitleID from tblXXXXXXXX";
OleDbDataAdapter adapter = new OleDbDataAdapter(sql, conn);
OleDbCommandBuilder cmdb = new OleDbCommandBuilder(adapter);
DataTable dt = new DataTable();
adapter.Fill(dt);
comboBox1.DataSource = dt;
comboBox1.DisplayMember = "Titles";
comboBox1.ValueMember = "Titles";
this.BindingContext[dt, "Titles"].Position = 0;
}
Hope this helps.
Excellence is doing ordinary things extraordinarily well.
|
|
|
|
|
Dankie Kwagga,
I've never actually used a DataAdapter, I don't know why. So I'll definitely give this a try, thanks.
|
|
|
|
|
ok,
so here is what i am trying to accomplish, and i've had some "OK" ideas, but none seem to fit the bill exactly...
Program Logic:
i have a file, that will be read and parsed into a datatable
(this is at runtime, columns are unknown & generated as the file as parsed... the number of columns can change..)
then in my application, a certain set of criteria will be applied to that file, if col1 = "asdf", if col2 = "blue"
if all the conditions are met, the file is moved to dir A, if the conditions are not met, the file is moved to dir B.
Problem:
the problem comes when the criteria are applied, basically i want the end user to be able to create their own criteria for the file, the end user will not know SQL so i was thinking some kind of graphical representation of the WHERE clause....
there are a couple of problems i've ran into:
how would the user specify AND/OR to multiple conditions: (they can have infinite #)
(graphically represented:
IF col1 = "BLUE" AND
IF col2 = "Green" OR
IF col3 = "yellow"
could render 2 sets SQL Where clauses:
1. WHERE ((col1='blue' AND col2='green') OR col3='yellow')
2. WHERE (col1='blue' AND (col2='green' OR col3='yellow')
my solution for this problem was to setup AND/OR condition groups:
Graphically represented:
IF all of the following are true
(
col1='blue'
col2='green'
)
OR
IF all of the following are true
(
col3='yellow'
)
this is easy to represent graphically, but i can't find a good solution for storing it long term in the database...
i'd rather not have to write an entire application to generate/parse SQL into this format
does anyone have any ideas? / are the some code snippets available that do something similar?
|
|
|
|
|
I'm not sure of all you're proposing, but I never allow data from a file to be loaded into a database simply based on the sender's say-so. I've been asked to implement such things more than once. Don't give out information willy-nilly -- the sender shouldn't know the names of the columns in the table, nor even what database system you use.
I very much prefer to have a method of validation and mapping under my own care that directs the file import process.
|
|
|
|
|
in a standard database-type system this is true, however the entire point of the application is moving files from one folder to either of two ending folders, so the datatable i mentioned is just a temporary one.
|
|
|
|
|
You need to develop what's called an ad-hoc query interface. I'd probably create a form that contained the following controls in a row:
Label (with column name)
ComboBox (allows the user to select an operator, like <, = >, etc - "=" is the default selection)
TextBox (allows the user to specify the value used in the expression)
ComboBox (allows the user to specify END, AND or OR - END is the default selection)
If the user selected AND or OR in the last combobox, add another row of controls to the form.
When the user indicates that he's done specifying parameters, create a LINQ query that conforms to the specified parameters.
".45 ACP - because shooting twice is just silly" - JSOP, 2010
-----
You can never have too much ammo - unless you're swimming, or on fire. - JSOP, 2010
-----
"Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass." - Dale Earnhardt, 1997
|
|
|
|
|
ah, i knew it must have a name!!
that makes sense, and i have come to that conclusion, but i want to make it very advanced, and allow the user to have the ability for nested AND/OR clauses to produce SQL like this:
WHERE (col1 = "a" OR ((col2="b" or col3 = "c") AND (col4="d"))
is there an example of an ad-hoc query engine on codeproject, that i could look at?
|
|
|
|
|
Do you have the ability to type "google.com" in your browser's address bar?
".45 ACP - because shooting twice is just silly" - JSOP, 2010
-----
You can never have too much ammo - unless you're swimming, or on fire. - JSOP, 2010
-----
"Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass." - Dale Earnhardt, 1997
|
|
|
|
|
In my opinion, a better answer would be...
No I don't, but I'm sure a Google search will yield some useful results.
Says the same thing but without the unnecessary rudeness 
|
|
|
|
|
Of course, you're assuming I wanted to avoid being rude, or that I wasn't matter-of-factly posing a reasonable question.
".45 ACP - because shooting twice is just silly" - JSOP, 2010
-----
You can never have too much ammo - unless you're swimming, or on fire. - JSOP, 2010
-----
"Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass." - Dale Earnhardt, 1997
|
|
|
|
|
John Simmons / outlaw programmer wrote: Of course, you're assuming I wanted to avoid being rude, or that I wasn't matter-of-factly posing a reasonable question
you don't think i have searched google?, i actualy assumed that the user answering the thread would have some more in depth knowledge other than "this is what its called..."
there is no need to be rude, that only gives yourself a bad name.
|
|
|
|
|
There is a function with byte** parameter taking array of pointers to byte array.
How to pin pointers to managed list of byte[] arrays and pass it that unmanaged function?
Чесноков
|
|
|
|
|
You pin a byte[] by using the fixed keyword within an unsafe code block
Please also refer to CP article:
This[^]
|
|
|
|
|
That is not single byte[] array.
There is a list of byte[] arrays List<byte[]>.
The unmanaged function takes byte** argument the array of pointers to byte* arrays.
Чесноков
|
|
|
|
|
Can you show us the signature of the unmanaged function?
|
|
|
|
|
I forgot how to handle that situation in C#.
It needs to allocate with static alloc array of pointers then pin byte[] from List to that array.
void function(byte** data, unsigned int N, unsigned int M)
{
for (int i = 0; i < N; i++)
{
for (int j = 0; j < M; j++)
printf("%c ", data[i][j]);
printf("\n");
}
}
The functions takes array of pointers to byte* arrays.
In C# those byte[] arrays are stored in the List<byte[]> collection.
Чесноков
|
|
|
|
|
I would try calling ToArray() on the List<byte[]> and passing the result.
It should work as an array is a reference type so it should be a pointer to an array of pointers.
|
|
|
|
|
That is not the interaction between 2 managed modules.
What will you do with byte[][] to pass it to unmanaged function taking byte** as argument?
Чесноков
|
|
|
|
|
Ok, I have not tested it, but if the lst object is a List<byte[]>, this is the easiest way:
byte[][] arr = lst.ToArray<byte[]>();
And then pass the arr object to the function if you have imported it setting byte[][] as the type for the first parameter, and you have to make sure that each byte[] array into the List<byte[]> has the same length.
As I said, I have not tested it. Tell us if it does not work, becouse there is another way, though it is a little more tricky.
|
|
|
|
|
.NET will never allow to pass byte[][] to byte** parameter 
Чесноков
|
|
|
|
|
Errrr, I think I've got lost somewhere... I was speaking about P/Invoke. What are you speaking about?
|
|
|
|
|
PInvoke.
It is not possible to pass managed byte[][] to unmanaged byte**.
Even if it was possible managed memory is not fixed.
I have List<byte[]> and I need to pass it to byte**.
byte[][] conversion is out of scope as arrays may be of different size.
It needs to allocate with static alloc array to hold pinned pointers. Then to pin them.
I do not remeber how to do it.
Чесноков
|
|
|
|
|
Ok. Let's see.
Chesnokov Yuriy wrote: It is not possible to pass managed byte[][] to unmanaged byte**.
This possibility depends on how you import the unmanaged function. When using P/Invoke the parameters in the managed version just need to have the same size of the target unmanaged version. Since byte** is a pointer, and byte[][] is a reference, both of them have the same size becouse both of them are pointers.
Chesnokov Yuriy wrote: Even if it was possible managed memory is not fixed.
Yes, that's right, but when you make a P/Invoke call, the CLR automatically pins the references passed to the unmanaged function into the managed heap, so the references will not move until the call is finished so, if you use references (such as byte[]), there is no need to manually pin them.
Chesnokov Yuriy wrote: I have List and I need to pass it to byte**.
Try importing the unmanaged function as I told you before, I mean, use byte[][] and not byte** as the type for the first parameter. Belive me, this is the easiest way, it's worth to try. We can try the tricky version later if this does not work.
Chesnokov Yuriy wrote: byte[][] conversion is out of scope as arrays may be of different size.
And casting to byte** is a warranty for that?
Chesnokov Yuriy wrote: It needs to allocate with static alloc array to hold pinned pointers. Then to pin them.
To pin references into the managed heap you have to use GCHandle struct.
|
|
|
|
|
_Erik_ wrote: Yes, that's right, but when you make a P/Invoke call, the CLR automatically pins the references passed to the unmanaged function into the managed heap, so the references will not move until the call is finished so, if you use references (such as byte[]), there is no need to manually pin them.
_Erik_ wrote: Try importing the unmanaged function as I told you before, I mean, use byte[][] and not byte** as the type for the first parameter. Belive me, this is the easiest way, it's worth to try. We can try the tricky version later if this does not work.
That is very intresting.
So far declaring DllImport for PInvoke stated to use native pointers and data types and use fixed every time. That actually compiled. It is a great relief to use managed types in PInvoke declarations instead of unmanaged with fixed statements.
However ToArray() produces the copy of the list. I do not want to spawn copies of the data.
Also is there guarantee that byte[][] array layout in managed memory is plain and there will be no access violation?
I need the ability to quickly pass byte[] objects to byte** array of pointers.
Those byte[] arrays can be stored in a List items or each byte[] array can be a Field in another object thus it is not possible to have ToArray on the list of those objects with those byte[] array items.
Чесноков
|
|
|
|
General 
News 
Suggestion 
Question 
Bug 
Answer 
Joke 
Praise 
Rant 
Admin 
Submit an article or tip
