3116 Top 10 Techniques for Microsoft.NET Framework Database Developers Cary Jensen President Jensen Data Systems, Inc.

Overview 1. Expression DataColumns 2. Intermediate DataColumn Expressions 3. Navigating Programmatically 4. Creating Calculated Fields Programmatically 5. Understanding BindingManagers 6. Creating Data Modules 7. Using DataViews 8. Avoiding the SQL Script Hack 9. Synchronzing DataSets and XMLDocuments 10. Computing Expressions on Filtered DataTables

Field References in Expressions  Use the ColumnName property to reference fields  if ColumnName contains one of the following characters, the field reference must be enclosed in brackets: (space), \n (newline), \t (tab), \r (carriage return), ~, (, ), #, \, /, =, >, <, +, -, *, %, &, |, ^, ‘, “, [,]  For consistency, you can use brackets even when the column name does not include one of the special characters.  If your column name includes the ] character, it must be preceded by a \.

Field Reference Examples Column Name AccountNo Account# Last Name Column[1] Reference AccountNo [Account#] [Last Name] [Column[1\]]

Literals  Strings enclosed in single quotes ex: 'Mr ' + [Contact Name]  Dates enclosed between # characters: ex: [Date] - #1/1/2004#  Numeric values, including decimal values and scientific notation, are not delimited ex: [Percent] * 100

String Literals and Delphi Consider the following string assignment (in C#): dataColumn1.Expression = "'Mr ' + [First Name] + ' ' + [Last Name] "; String literals are more complicated for Delphi developers, since single quotes are already used to delimit strings. For example: DataColumn1.Expression := '''Mr ''' + ' + [First Name] + ' + ''' ''' + ' + [Last Name]'; You can also use the QuotedStr function in Borland.Vcl.SysUtils: DataColumn1.Expression := QuotedStr('Mr ') + ' + [First Name] + ' + QuotedStr(' ') + ' + [Last Name]'; Alternatively, enclose string literals between #39, like this: DataColumn2.Expression := #39 + 'Mr ' + #39 + ' + [Invoice No] + ' + #39 + ' ' + #39 + ' + [Customer ID]'; You can even omit the concatenation operator (+) between #39 and strings: DataColumn2.Expression := #39'Mr '#39' + [Invoice No] + '#39' '#39' + [Customer ID]';

Comparison operators (in order of precedence) < > <= >= <> = IN LIKE

Boolean Operators ( expression) AND OR NOT

Table Navigation

DataSets, DataTables, and DataRows r1c1r1c2r1c3r1c4r1c5 r2c1r2c2r2c3r2c4r2c5 r3c1r3c2r3c3r3c4r3c5 DataSet var Table: DataTable; Row: DataRow; data: String; begin Table := DataSet1.Tables[0]; Row := Table.Rows[2]; data := Row[1].ToString(); r1c1r1c2r1c3r1c4r1c5 r2c1r2c2r2c3r2c4r2c5 Table1 Table2

DataSets, DataTables, and DataRows r1c1r1c2r1c3r1c4r1c5 r2c1r2c2r2c3r2c4r2c5 r3c1r3c2r3c3r3c4r3c5 DataSet var data: String; begin data := DataSet1.Tables[0].Rows[2][1].ToString(); //or data := DataSet1.Tables[0].Rows[2][‘rowname’].ToString(); r1c1r1c2r1c3r1c4r1c5 r2c1r2c2r2c3r2c4r2c5 Table1 Table2

Programmatically Create Calculated Fields  Create a DataColumn in your DataTable that will hold the calculated field  After loading data, iterate through the DataTable and assign the calculation. Then make the calculated field to readonly  Add a ColumnChanged event handler to the DataTable  From the ColumnChanged event handler, test whether the changed field is one of those involved in the calculation. If so, make the calculated field writeable, re-calculate the calculation, then make the field readonly once again

Controls and CurrencyManagers  All controls, that is, classes that descend from Control in the.NET FCL, are data aware, and can be bound to a data source. A BindingManagerBase instance is created anytime a control is bound to a new data source.  Controls that are bound to the same data source are bound to the same BindingManagerBase instance. BindingManagerBase is an abstract class, and two concrete classes descend from it. These concrete classes are CurrencyManager and PropertyManager.

Creating a Data Module  Create a form that will serve as the data module (let’s call this form the data module) Add the ADO.NET components that you want to share to the public section of the data module's class declaration.  When the data module is created, create the instances of, and configure, the ADO.NET classes that you added to the form's public section  Add one Control descendant to the data module for each data source that you want to use in other forms. Bind each control to the data source you want to expose.  Declare a variable of the data module class type within scope of each form that must use a data module data source  For each form that uses the data module, assign that form’s BindingContext property to the data module's (form-level) BindingContext property.  For each Control descendant on each form, set the binding context (or DataSource and DataMember properties) to the appropriate data source on the data module.

Questions?

Thank You 3116 Top 10 Techniques for Microsoft.NET Framework Database Developers Please fill out the speaker evaluation You can contact me further at …