Sunwen Tutorials----C # advanced (eight)

What I'm going to talk about in this section is that we are very concerned about, and certainly very interested in. Hey, it's also my favorite part of writing tutorials----ADO database access. Think of this, I think I wrote in last year's "access to the database" series of articles, Hey! If you think it's difficult to understand the record set, I recommend you look at my articles first. All right, let's get started!

What is ADO (ActiveX Data Objects), ADO is a very simple idea, an idea that allows you to access data in just one way. ADO is not a new idea, only the use of existing data access technology, the integration of it. If you don't understand ADO, think of ODBC! In fact, we are engaged in the ASP, the use of ADO, remember, that once we used countless times set conn= Server.CreateObject ("ADODB. Connection ")? Yes, it is. As for some of the conceptual nature of ADO, please consult the information on their own, but, in fact, do not understand it does not matter, just think of it as a m$ to our data access to the tool bar!

OK, the following example is based on a m$ Access 2000 database, its structure is as follows, the table name is categories, the file name is Bugtypes.mdb, quickly build a bar:

Category ID Category Name
1 Bugbash Stuff
2 Appweek Bugs
3. NET Reports
4 Internal Support

OK, I'll write all the programs first, and then we'll have a taste of one sentence:

From://Ado\adosample.cs
001:using System;
002:using System.Data;
003:using System.Data.ADO;
004:
005:public class MainClass
006: {
007:public static void Main ()
008: {
009://Set the connection string and select the command string 010:string straccessconn = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=bugtypes.mdb";
011:string straccessselect = "SELECT * from Categories";
012:
013://Create a record set and fill in the Categories form
014:dataset myDataSet = new DataSet ();
015:mydataset.tables.add ("Categories");
016:
017://Establish ADO instance 018:adoconnection Myaccessconn = new ADOConnection (straccessconn);
019:adodatasetcommand myaccessdatasetcmd = new Adodatasetcommand ();
020:myaccessdatasetcmd.selectcommand = new Adocommand (straccessselect,myaccessconn);
021:
022:myaccessconn.open ();
023:try
024: {
025:myaccessdatasetcmd.filldataset (myDataSet, "Categories");
026:}
027:finally
028: {
029:myaccessconn.close ();
030:}
031:
032:try
033: {
034://A Recordset can contain multiple tables, and we put them in an array 035:datatable[] dta = myDataSet.Tables.All;
036:foreach (DataTable DT in DTA)
037: {
038:console.writeline ("Found data table {0}", dt. TableName);
039:}
040:
041://The following two lines show two ways to get the number of tables in this dataset from one recordset
042:console.writeline ("{0} tables in data set", MyDataSet.Tables.Count);
043:console.writeline ("{0} tables in data set", DTA. Length);
044://The following lines show how to rely on the name of a table to get information from a recordset
045:console.writeline ("{0} rows in Categories table", mydataset.tables["Categories"]. Rows.Count);
046://Column information is automatically obtained from the database, so we can use the following code 047:console.writeline ("{0} columns in Categories table", mydataset.tables[" Categories "]. Columns.count);
048:datacolumn[] DRC = mydataset.tables["Categories"]. Columns.all;
049:int i = 0;
050:foreach (DataColumn DC in DRC)
051: {
052://Print out subscript and column names and data type 053:console.writeline ("column name[{0}] is {1}, of type {2}", i++, DC. ColumnName, DC. DataType);
054:}
055:datarow[] dra = mydataset.tables["Categories"]. Rows.all;
056:foreach (DataRow Dr in Dra)
057: {
058://Print out CategoryID and CategoryName059:Console.WriteLine ("categoryname[{0}" is {1} ", Dr[0], dr[1]);
060:}
061:}
062:catch (Exception e)
063: {
064:console.writeline ("Oooops. Caught an exception:\n{0} ", E.message);
065:}
066:}
067:}
It seems that this example is a bit complicated, just blame me for choosing the bad, hehe. However, it is understandable to analyze it carefully. Let me now say a few of the special things in this example. The first is not like in ASP, A command string is required to be treated as a Command object. 020 It's just this thing. Note that there is a myDataSet.Tables.Add ("Categories") statement in line 015, which does not fill in the Categories table in the database. Just build an empty table, and 025 is the real fill.

The output of this example is:

Found data Table Categories
1 tables in Data set
1 tables in Data set
4 Rows in Categories table
2 Columns in Categories table
Column Name[0] is CategoryID, of type Int32
Column Name[1] is CategoryName, of type System.String
CATEGORYNAME[1] is bugbash stuff
CATEGORYNAME[2] is Appweek Bugs
CATEGORYNAME[3] is. NET Reports
CATEGORYNAME[4] is Internal support
Well, that's it, Sunwen really want to sleep, what music is no use, hehe. This example really takes a lot of effort to fully understand. o.k.886!

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