I want to load the entire database (SQL Server) I have into a dataset so that I can work with several tables and their relationships. I know this might be frowned upon, but how can I do this (I will be using DataRelation and Table objects)?
Thanks
Unless I'm missing something this should just be a simple case of generating a dataset and then altering the Fill methods to remove the WHERE portion. Then ensure you call the fills in the right order (master, then detail) to ensure you maintain the referential integrity.
You can run this... but don't expect to have a db or app server after.
using (SqlConnection conn = new SqlConnection("YourConnectionString"))
{
using (SqlCommand command = new SqlCommand("exec sp_msforeachtable 'select * FROM ?'", conn))
{
conn.Open();
DataSet ds = new DataSet();
command.Fill(ds);
}
}
Read some article about in memory Database.
# Randolph Potter idea is an option - you can get the list of tables from the server, and then iterate on the list and load all the tables. I guess you can do that same about FK and relations.
you can probably do it automatically using the designer - using drag and drop from the server explorer to a dataset (VS2008), and with a little code load the entire thing into memory.
I suppose you could do multiple selects within a single stored procedure and then fill a dataset.
using (SqlConnection conn = new SqlConnection("YourConnectionString"))
{
using (SqlDataAdapter command = new SqlDataAdapter("usp_YourStoredProcedure", conn))
{
command.CommandType = CommandType.StoredProcedure;
conn.Open();
DataSet ds = new DataSet();
command.Fill(ds);
}
}
I would agree with the other comments here that unless your database is tiny this is a really bad idea.
Related
I have tried to retrieve data from my table on MySql using my C# application. So I applied the usual connection methods in order to connect my c# application to my MySql database and also called to appropriate methods to retrieve the data from the table and then display it on my application. However, I noticed that by just using the following code :
conString = "server=localhost;user id=" + user + ";database=db;password="+pass;
connection = new MySqlConnection(conString);
DataTable table = new DataTable();
MySqlDataAdapter adapter = new MySqlDataAdapter("SELECT * FROM users", connection);
adapter.Fill(table);
dataGridView1.DataSource = table;
I can retrieve the data from the table and display, without using the following code:
connection.Open();
what is the purpose to use connection.Open() if I only need the following code to retrieve data? When will I need to use connection.Open() ?
Do I need to use connection.Open() only when I sending information from my application to mysql but when I want to get/retrieve information from MySql then I don't need to use connection.Open(), is this correct?
Since the intention of calling adapter.Fill(table); is to retrieve data from the database I would highly expect that the Fill method opens the connection if it isn't already.
You would only need to explicitly call Open if you intend to operate on the connection directly instead of through helper classes like MySqlDataAdapter for example. You can of course open it whenever you feel like.
I would, however, suggest you put the connection in a using statement to ensure that it's closed and disposed of when you are done with it:
using (var connection = new MySqlConnection(conString))
{
DataTable table = new DataTable();
MySqlDataAdapter adapter = new MySqlDataAdapter("SELECT * FROM users", connection);
adapter.Fill(table);
dataGridView1.DataSource = table;
}
// Now you are sure the connection is closed and being properly garbage collected
I'm using Microsoft SQL Server 2008 R2 and asp.net for C#.
Currently I'm doing an intranet. It consists of many modules inside intranet. Each module uses its own database. Normally I will using connection string for calling to the database.
I plan to do a main page to manage all pending tasks inside each module. Means on the main page, I will show all the pending tasks of all modules. Since they are all using different connection strings, what approaches can be used to achieve this?
The example below show how I access database through single connection string:
string connectionString = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
string strsql = " select * from User ";
SqlConnection con = new SqlConnection(connectionString);
SqlDataAdapter da = new SqlDataAdapter(strsql, connectionString);
con.Open();
DataSet ds = new DataSet();
da.Fill(ds);
con.Close();
con.Dispose();
Create a proc where you can call table of different database with respective Db names.
create proc proc_name
as begin
select * from [DB_name1].dbo.tablename
union all
select * from [DB_name2].dbo.tablename
end
now call the proc from your code behind.
No matter what ever db name in your connection string,still you can access
Note: check your DB has rights to access other DB.
I'm developing a C# application and I want to copy a whole table from a SQL Server CE database to another programmatically. I know I can use this command in SQL Server, but I'm not sure how to use two database connections in one query in C#.
Select * into DestinationDB.dbo.tableName from SourceDB.dbo.SourceTable
Thanks in advance.
You wouldn't do it the same way as in SQL Server because there's no single server that manages both databases. Your app is the only thing that links the two databases so the the data has to go through your app. You're trying to do it the wrong way and that's why you can't find a solution: you're looking for the wrong thing.
There are examples of this out there. I know, because I've written more than one myself. You simply need to use a data adapter to populate a DataTable from the first database and then a data adapter to save the contents of that DataTable to the second database. If the data sources are the same type then you can even use just one data adapter because the SelectCommand and InsertCommand can have different connections.
using (var adapter = new SqlDataAdapter("SELECT statement here", "source connection string here"))
using (var destinationConnection = new SqlConnection("destination connection string here"))
using (var insertCommand = new SqlCommand("INSERT statement here", destinationConnection))
{
// Add parameters to insertCommand here.
adapter.InsertCommand = insertCommand;
// Leave the RowState of all DataRows as Added so they are ready to be inserted.
adapter.AcceptChangesDuringFill = false;
var table = new DataTable();
// Retrieve data from source and save to destination.
adapter.Fill(table);
adapter.Update(table);
}
That example uses SqlClient but it works the same for any provider, including SqlServerCe.
I have a C#/ASP.net project has included a database that I have developed that includes a nice and convenient View that would be handy to use.
I have the SQL connection setup to a SQL Server 2008 DB I created. It seems as though it is connecting fine, but I don't understand how to actually use the View that I created without hard coding the query into the program (been told this is bad sometimes?).
This is my connection I setup:
SqlConnection conn = null;
conn = new SqlConnection("Data Source=raven\\sqlexpress;Initial Catalog=ucs;Integrated Security=True;Pooling=False");
conn.Open();
SqlCommand command = new SqlCommand(query, conn);
Basically, I need some code to query using this View. I can see the View and look at the results that would be obtained, but not access it in the program!
The view is named "UserView". Help is much appreciated!
You could use something like the following. But it's usually considered evil to put hardcoded SQL commands into .Net code. It's much better and safer to use stored procedures instead.
This should get you started. You can modify it to use stored procedures by
changing the command.CommandType to indicate it's a stored proc call
And adding the proper parameters to the command that your SP needs.
Change command.CommandText to the name of your SP, thus
eliminating the hardcoded SQL.
sample code below:
using (SqlConnection connection = new SqlConnection("Data Source=raven\\sqlexpress;Initial Catalog=ucs;Integrated Security=True;Pooling=False"))
{
using (SqlCommand command = connection.CreateCommand())
{
command.CommandText = "SELECT * from your_view WHERE your_where_clause";
connection.Open();
using (SqlDataReader reader = command.ExecuteReader())
{
while (reader.Read())
{
// process result
reader.GetInt32(0); // get first column from view, assume it's a 32-bit int
reader.GetString(1); // get second column from view, assume it's a string
// etc.
}
}
}
}
Using VS2013 add a new DataSet to your project. Drag your View from the Server Explorer to the DataSet Design Surface.
ok now i am using the SQL database to get the values from different tables... so i make the connection and get the values like this:
DataTable dt = new DataTable();
SqlConnection connection = new SqlConnection();
connection.ConnectionString = ConfigurationManager.ConnectionStrings["XYZConnectionString"].ConnectionString;
connection.Open();
SqlCommand sqlCmd = new SqlCommand("SELECT * FROM Machines", connection);
SqlDataAdapter sqlDa = new SqlDataAdapter(sqlCmd);
sqlCmd.Parameters.AddWithValue("#node", node);
sqlDa.Fill(dt);
connection.Close();
so this is one query on the page and i am calling many other queries on the page.
So do i need to open and close the connection everytime...???
also if not this portion is common in all:
DataTable dt = new DataTable();
SqlConnection connection = new SqlConnection();
connection.ConnectionString = ConfigurationManager.ConnectionStrings["XYZConnectionString"].ConnectionString;
connection.Open();
can i like put it in one function and call it instead.. the code would look cleaner...
i tried doing that but i get errors like:
Connection does not exist in the current context.
any suggestions???
thanks
You can definitely share the "open connection" code, no reason to duplicate it.
With the SQL Server provider for ASP.NET, there is very little overhead with "closing" the connection every time. It just returns the connection to your process' connection pool (see here), so opening the next connection will use very little overhead. I think it is good practice to close the connection after each operation
I use "using". You can include as many queries as you like inside. When complete it will clean up for you.
using (SqlConnection cn = new SqlConnection(connectionString))
{
using (SqlCommand cm = new SqlCommand(commandString, cn))
{
cn.Open();
cm.ExecuteNonQuery();
}
}
Typically yes, you make individual connections for multiple rowsets.
If you can use joins to produce a single meaningful rowset, that's typically a good thing to do on the server side instead of the client side.
You may also want to look at making multiple connections and using the async features in order to queue all your requests simultaneously instead of sequentially - have a look at this article.
No you do not have to open and close the connection every time as long as you are using the same database. What you need to change is the
sqlCommand's queryString every time.
Like what #durilai said, [using] is useful. Using actually has more functions than this, but essentially it puts a try/catch block around your code and calls dispose to close the connection in this case.
Anything that needs open/close can be used with using, so things such as text writers, or other objects.