Overcoming Keyword Conflicts When Using CommandBuilders

Chia sẻ: Bui Tuan | Ngày: | Loại File: PDF | Số trang:4

Thêm vào BST

Báo xấu

76
lượt xem 4
download

Download Vui lòng tải xuống để xem tài liệu đầy đủ

[ Team LiB ] Recipe 4.14 Overcoming Keyword Conflicts When Using CommandBuilders Problem Your data includes table and column names that conflict with SQL keywords. You can overcome this with brackets or quotes in SELECT statements that you write, but the CommandBuilder creates illegal update statements.

Chủ đề:

Bình luận(0) Đăng nhập để gửi bình luận!

Lưu

Nội dung Text: Overcoming Keyword Conflicts When Using CommandBuilders

[ Team LiB ] Recipe 4.14 Overcoming Keyword Conflicts When Using CommandBuilders Problem Your data includes table and column names that conflict with SQL keywords. You can overcome this with brackets or quotes in SELECT statements that you write, but the CommandBuilder creates illegal update statements. You need to know how to use the CommandBuilder with your data. Solution Use the QuotePrefix and QuoteSuffix properties of the CommandBuilder object to delimit database server object names containing spaces or other illegal characters. The sample code contains two event handlers: Preview Button.Click Displays the delete, insert, and update commands using the delimiters specified by the user for the QuotePrefix and QuoteSuffix properties, and either the OLE DB or SQL Server data provider as specified by the user. Retrieve OLE DB Button.Click Uses the GetOleDbSchemaTable( ) method of the OleDbConnection object to retrieve the default prefix and suffix delimiters for the data source. The C# code is shown in Example 4-33. Example 4-33. File: CommandBuilderKeywordConflictForm.cs // Namespaces, variables, and constants using System; using System.Configuration; using System.Data; using System.Data.SqlClient; using System.Data.OleDb; // . . . private void previewButton_Click(object sender, System.EventArgs e) {
String sqlText = "SELECT OrderID, ProductID, Quantity, " + "UnitPrice, Discount FROM [Order Details]"; if (oleDbRadioButton.Checked) { // Build the DataAdapter and the CommandBuilder. OleDbDataAdapter da = new OleDbDataAdapter(sqlText, ConfigurationSettings.AppSettings["OleDb_ConnectString"]); OleDbCommandBuilder cb = new OleDbCommandBuilder(da); // Set the prefix and suffix. cb.QuotePrefix = quotePrefixTextBox.Text; cb.QuoteSuffix = quoteSuffixTextBox.Text; // Display CommandBuilder commands with the prefix and suffix. resultTextBox.Text = "DeleteCommand: " + cb.GetDeleteCommand( ).CommandText + Environment.NewLine + Environment.NewLine + "InsertCommand: " + cb.GetInsertCommand( ).CommandText + Environment.NewLine + Environment.NewLine + "UpdateCommand: " + cb.GetUpdateCommand( ).CommandText; } else { // Build the DataAdapter and the CommandBuilder. SqlDataAdapter da = new SqlDataAdapter(sqlText, ConfigurationSettings.AppSettings["Sql_ConnectString"]); SqlCommandBuilder cb = new SqlCommandBuilder(da); // Set the prefix and suffix. cb.QuotePrefix = quotePrefixTextBox.Text; cb.QuoteSuffix = quoteSuffixTextBox.Text; // Display CommandBuilder commands with the prefix and suffix. resultTextBox.Text = "DeleteCommand: " + cb.GetDeleteCommand( ).CommandText + Environment.NewLine + Environment.NewLine + "InsertCommand: " + cb.GetInsertCommand( ).CommandText + Environment.NewLine + Environment.NewLine + "UpdateCommand: " + cb.GetUpdateCommand( ).CommandText; } }
private void retrieveOleDbButton_Click(object sender, System.EventArgs e) { // Retrieve the quote prefix and suffix for the server. OleDbConnection conn = new OleDbConnection( ConfigurationSettings.AppSettings["OleDb_ConnectString"]); conn.Open( ); DataTable tableSchema = conn.GetOleDbSchemaTable(OleDbSchemaGuid.DbInfoLiterals, new object[] {}); conn.Close( ); // Set the primary key to enable find on LiteralName column. tableSchema.PrimaryKey = new DataColumn[] {tableSchema.Columns["LiteralName"]}; // Get the prefix and suffix from the OleDbLiteral enumeration. DataRow row; row = tableSchema.Rows.Find("Quote_Prefix"); quotePrefixTextBox.Text = ((row == null) ? "" : row["LiteralValue"].ToString( )); row = tableSchema.Rows.Find("Quote_Suffix"); quoteSuffixTextBox.Text = ((row == null) ? "" : row["LiteralValue"].ToString( )); } Discussion The QuotePrefix and QuoteSuffix properties of the CommandBuilder object specify the beginning and ending characters used to delimit database server object names, such as tables and columns in the updating commands generated by the CommandBuilder. This is necessary when the object names contain special characters or reserved tokens; otherwise, the commands will fail when executed. For example, in SQL Server 2000 and later, database object names can contain any valid Microsoft Windows NT/2000/XP character including spaces and punctuation marks. T- SQL is more restrictive with identifiers that can be used without delimiters. You can use QuotePrefix and QuoteSuffix to delimit the SQL Server object names when required by T-SQL. The QuotePrefix and QuoteSuffix values have no effect on the CommandText of SelectCommand. These delimiters must be specified as part of the SelectCommand that the CommandBuilder is based on.
The default values for QuotePrefix and QuoteSuffix are empty strings. The example demonstrates using QuotePrefix and QuoteSuffix with both the OLE DB and SQL Server CommandBuilder objects. As you can see, they function nearly identically. The CommandBuilder makes it easy to update the data source with changes made to the DataSet. Update logic is created automatically so no understanding is required of how to code the actual delete, insert, and update SQL statements. The CommandBuilder drawbacks include slower performance because of the time that it takes to request metadata and construct the updating logic, updates that are limited to simple single-table scenarios, and a lack of support for stored procedures. Because of these drawbacks, the CommandBuilder is seldom used in enterprise application development. The example also demonstrates retrieving the default quote prefix and suffix from the database server. The GetOleDbSchemaTable( ) method of the OleDbConnection object returns schema information from a data source based on a GUID argument indicating one of the OleDbSchemaGuid values. The value DbInfoLiterals returns a list of provider- specific literals used in text commands. The literals are returned as a table of rows. Within this table, there is a column named LiteralName. The rows containing the default values for the quote prefix and suffix are identified by a LiteralName value of Quote_Prefix and Quote_Suffix, respectively. The actual values are stored in the LiteralValue column. [ Team LiB ]