replace.pretilute.com |
||
.NET/Java PDF, Tiff, Barcode SDK LibraryYou can execute a simple SQL command to create a table; all you need is to specify its data fields and their types and whether null values are allowed. In the following example, we create an Employees table with a primary key EmpID and FirstName, LastName, and Birthday fields. execNonQuery conn "CREATE TABLE Employees ( EmpID int NOT NULL, FirstName varchar(50) NOT NULL, LastName varchar(50) NOT NULL, Birthday datetime, PRIMARY KEY (EmpID))" We can now insert two new records as follows: execNonQuery conn "INSERT INTO Employees (EmpId, FirstName, LastName, Birthday) VALUES (1001, 'Joe', 'Smith', '02/14/1965')" execNonQuery conn "INSERT INTO Employees (EmpId, FirstName, LastName, Birthday) VALUES (1002, 'Mary', 'Jones', '09/15/1985')" and retrieve two columns of what was inserted using a fresh connection and a data reader: let query() = seq { use conn = new SqlConnection(connString) do conn.Open() use comm = new SqlCommand("SELECT FirstName, Birthday FROM Employees", conn) use reader = comm.ExecuteReader() while reader.Read() do yield (reader.GetString 0, reader.GetDateTime 1) } When we evaluate the query expression in F# Interactive, a connection to the database is created and opened, the command is built, and the reader is used to read successive elements: print qr code vb.net, barcodelib.barcode.winforms.dll download, winforms code 128, vb.net gs1 128, vb.net ean-13 barcode, pdf417 vb.net, c# remove text from pdf, pdfsharp replace text c#, vb.net generate data matrix code, itextsharp remove text from pdf c#,Table 7-7 lists six different combinations of result set categories available in Oracle, along with their capabilities. Table 7-7. Different Result Set Categories and Their Capabilities > fsiAddPrinter(fun (d: SystemDateTime) -> dToString());; val it : unit = () > query();; val it : seq<string * SystemDateTime> = seq [("Joe", 14/02/1965 00:00:00); ("Mary", 15/09/1985 00:00:00)] The definition of query uses sequence expressions that locally define new IDisposable objects such as conn, comm, and reader using declarations of the form use var = expr These ensure that the locally defined connection, command, and reader objects are disposed after exhausting the entire sequence See s 4, 8, and 9 for more details on sequence expressions of this kind F# sequences are on-demand (that is, lazy), and the definition of query does not itself open a connection to the database This is done when the sequence is first iterated, and indeed a connection is maintained until the sequence is exhausted. Here is the markup from CreateSessionVars.aspx. <%@ Page language="c#" CodeFile="CreateSessionVars.aspx.cs" Inherits="CreateSessionVars" %> <HTML> <HEAD> <title>CreateSessionVars</title> </HEAD> <body> <form id="Form1" method="post" runat="server"> How many variables <asp:TextBox Runat=server id=txtCount text=0 /> <asp:CompareValidator runat=server ControlToValidate=txtCount Operator=DataTypeCheck Type=Integer ErrorMessage='Must be an integer' Display=Dynamic /> <br><br> <asp:Button Runat=server ID=btnSubmit Text='Create them' /><br><br> <asp:Label Runat=server ID=lblOutput /> </form> </body> </HTML> And here are the Button Click and PreRender events from the code-behind of CreateSessionVars.aspx.cs. private void btnSubmit_Click(object sender, System.EventArgs e) { int Count = int.Parse(txtCount.Text) + Session.Keys.Count; for (int i = Session.Keys.Count; i < Count; i++) { Session[string.Format("sessionvar{0}",i)] = i; } } private void CreateSessionVars_PreRender(object sender, EventArgs e) { lblOutput.Text = string.Format( "Session count at start of request: {0}<br>" + "Session count at end of request: {1}<br>", this.SessionVarCount, Session.Keys.Count); } Since the preprocessor passes the session variable count into the Page property each time the page is requested, here s how the page renders after a 1 is posted back to the server (see Figure 2-3). Forward-only/read-only (default) Note that the command object s ExecuteReader method returns a DataReader instance that is used to extract the typed data returned from the query You can read from the resulting sequence in a straightforward manner using a sequence iterator For instance, we can use a simple anonymous function to print data on the screen: > query() |> Seqiter (fun (fn, bday) -> printfn "%s has birthday %O" fn bday);; Joe has birthday 14/02/1965 00:00:00 Mary has birthday 15/09/1985 00:00:00 val it : unit = () The query brings the data from the database in-memory, though still as a lazy sequence You can then use standard F# in-memory data transformations on the result: > query() |> Seqfilter (fun (nm, bday) -> bday < SystemDateTimeParse("01/01/1985")) |> Seq. Not scrollable. Cannot perform insert, update, and delete operations on the ResultSet object. Cannot detect any changes made to the database while the ResultSet is open. Scrollable. Does not automatically detect certain changes made to the database while the ResultSet is open. Cannot perform insert, update, and delete operations on the ResultSet object. Scrollable. Limited ability to detect certain changes made to the underlying ResultSet data in the database. Cannot perform insert, update, and delete operations on the ResultSet object. Not scrollable. Can perform insert, update, and delete operations on the ResultSet object. Scrollable. Does not automatically detect certain changes made to the database while the ResultSet is open. Can perform insert, update, and delete operations on the ResultSet object. Scrollable. Limited ability to detect certain changes made to the underlying ResultSet data in the database. Cannot perform insert, update, and delete operations on the ResultSet object. Figure 2-3. The CreateSessionVars page on its second rendering And then, after the first postback, here s the same page after a 3 is posted back (see Figure 2-4).
|
||