ITS 328 CHAPTER 3: STORING DATA IN MEMORY 1

Storing Data in Memory After today you will be able to: ◦Explain how a DataTable stores data ◦Add new data rows to a table ◦Examine, update, and remove existing values in a table row ◦Explain how ADO.NET differentiates between pending and final data values ◦Integrate data verification code into your DataTable object 2

Today’s Exercise Chapter 3 CSharp Project ◦Open Chapter 3 CSharp.sln in files folder Add DataRow programmatically (p.41) Fill Form Display Fields (p.43) Edit a DataRow (p.43) Validating Content (p.54) 3

Creating a Table (Chapter 2) Create a Table ◦DataTable someTable = new DataTable("Customer"); Add a Column ◦someTable.Columns.Add("ExpireDate", typeof(DateTime)); Add Column with Constraints ◦DataColumn newColumn;// Use to specify properties ◦newColumn = someTable.Columns.Add("FullName", typeof(string)); ◦newColumn.MaxLength = 30; ◦newColumn.AllowDBNull = false; ◦newColumn.Unique = true; 4

Adding Constraints to Columns (Chapter 2) DataColumn newColumn;// Use to specify properties newColumn = someTable.Columns.Add("FullName", typeof(string)); newColumn.MaxLength = 30; newColumn.AllowDBNull = false; newColumn.Unique = true; newColumn.Caption = "Student Name"; 5

Adding Data Create a new row object ◦DataRow oneRow = someTable.NewRow(); Store the actual data values in the row object ◦oneRow.Item[2] = "Joe Schmoe"; ◦oneRow["FullName"] = "Joe Schmoe"; Add the row object to the table ◦someTable.Rows.Add(oneRow);// Adds to end of table ◦someTable.Rows.InsertAt(oneRow,0);// Inserts at beginning of table Add data directly, without row object ◦someTable.Rows.Add(new Object[] {1L, DateTime.Parse("12/31/2016"), "Joe Schmoe"}); 6

Exercise Part 1 – Adding Rows (P. 41) Open Chapter 3 CSharp project ◦Contains two Windows.Forms classes: AccountManager and AccountDetail Open AccountManager.cs (F7 from AccountManager Design window) Locate the Load Form event handler AccountManager_Load Review Creation of Table ◦oneColumn for adding constraints to columns ◦ColumnChanging event handlers for specifying business rules ◦Primary Key ◦Optional Columns 7

Exercise Part 1 – Adding Rows (P. 41) Below "// Build some sample data rows." comment, add: ◦CustomerAccounts.Rows.Add(new Object[] {1L, "Blue Yonder Airlines", true, 500m, DateTime.Parse("1/1/2007")}); ◦CustomerAccounts.Rows.Add(new Object[] {2L, "Fourth Coffee", true, 350m, DateTime.Parse("7/25/2009")}); ◦CustomerAccounts.Rows.Add(new Object[] {3L, "Wingtip Toys", false}); ◦Yourself active with a $100 annual fee starting tomorrow. Notice foreach adding Items to the AllAccounts ListBox component 8

Exercise Part 2 – Modifying Rows (P. 43) Examine ActAdd_Click() and ActEdit_Click() button event handlers ◦Each Invokes AccountDetail().EditAccount(ref editRecord, table) Open AccountDetail.cs [Design] ◦Load event handler fills the fields from DataRow from AccountManager ◦Properties and Events including AccountDetail Load event handler ◦Identify Components: AccountID, AccountName, AnnualFee, StartDate Arguments ◦eventRecord and CustomerAccounts are arguments from AccountManager ◦whichAccount and baseTable are parameters in AccountDetail ◦AccountEntry and AccountTable are instance names 9

Exercise Part 2 – Fill Form Code (P. 43) In AccountDetail_Load() add: if (AccountEntry != null) { AccountID.Text = string.Format("{0:0}", AccountEntry["ID"]); ActiveAccount.Checked = (bool)AccountEntry["Active"]; if (DBNull.Value.Equals(AccountEntry["FullName"]) == false) AccountName.Text = (string)AccountEntry["FullName"]; if (DBNull.Value.Equals(AccountEntry["AnnualFee"]) == false) AnnualFee.Text = string.Format("{0:0.00}", (decimal)AccountEntry["AnnualFee"]); if (DBNull.Value.Equals(AccountEntry["StartDate"]) == false) StartDate.Text = string.Format("{0:d}", (DateTime)AccountEntry["StartDate"]); } Search Google for "c# string.format" 10

Exercise Part 2 – Click OK Code (P. 43) Below workArea.BeginEdit(); add: workArea["Active"] = ActiveAccount.Checked; if (AccountName.Text.Trim().Length == 0) workArea["FullName"] = DBNull.Value; else workArea["FullName"] = AccountName.Text.Trim(); if (AnnualFee.Text.Trim().Length == 0) workArea["AnnualFee"] = DBNull.Value; else workArea["AnnualFee"] = decimal.Parse(AnnualFee.Text); if (StartDate.Text.Trim().Length == 0) workArea["StartDate"] = DBNull.Value; else workArea["StartDate"] = DateTime.Parse(StartDate.Text); 11

Deleting Rows Use Remove() or RemoveAt() methods to remove DataRow objects. Remove() accepts row instance as argument: ◦DataRow oneRow = someTable.Rows[0]; ◦someTable.Rows.Remove(oneRow); RemoveAt() accepts index position as argument ◦someTable.Rows.RemoveAt(0); Clear() removes all the rows ◦someTable.Rows.Clear(); 12

Batch Processing Allows a batch of changes before committing to any of them Preferable when changes occurring across multiple rows must be collectively valid After updates are complete ◦someTable.AcceptChanges();// Commit all row changes ◦someTable.RejectChanges();// Reject changes since last commit Use DataRow.BeginEdit() to postpone data checks and exceptions until DataRow.EndEdit(); 13

Exception-Based Errors Assigning data of the wrong data type to a column value. Supplying string data to a column that exceeds the maximum length defined in the column’s DataColumn.MaxLength property. Attempting to store a NULL value in a primary key column. Adding a duplicate value in a column that has its Unique property set. Operation that violates one of the table’s custom (e.g., relational) constraints. 14

Validation-Based Errors DataTable Column and Row Change Event Handlers ◦ColumnChanging, RowChanging, RowDeleting, TableNewRow ◦ColumnChanged, RowChanged, RowDeleted, TableClearing, TableCleared Example Check Age column for valid range: private void Applicant_ColumnChanging(Object sender, System.Data.DataColumnChangeEventArgs e) { // Check the Age column for a valid range. if (e.Column.ColumnName == "Age") { if ((int)e.ProposedValue 29) e.Row.SetColumnError(e.Column,"Applicant's age falls outside the allowed range."); } 15

Exercise Part 3 – Validate Content (P. 54) Follow the directions on Page 54 checking Annual Fee and Start Date. In the CustomerAccounts_ColumnChanging event handler, add: if (e.Column.ColumnName == "AnnualFee") { // Annual fee may not be negative. if (DBNull.Value.Equals(e.ProposedValue) == false) { if ((decimal)e.ProposedValue < 0m) e.Row.SetColumnError(e.Column, "Annual fee may not be negative."); } } else if (e.Column.ColumnName == "StartDate") { // Start date must be on or before today. if (DBNull.Value.Equals(e.ProposedValue) == false) { if (((DateTime)e.ProposedValue).Date > DateTime.Today) e.Row.SetColumnError(e.Column, "Start date must occur on or before today."); } 16

Exercise Part 3 – Validate Content (P. 54) In the CustomerAccounts_RowChanging event handler, add the following: if (e.Row.HasVersion(DataRowVersion.Proposed) == true) { if (((bool)e.Row["Active", DataRowVersion.Proposed] == true) && (DBNull.Value.Equals(e.Row["StartDate", DataRowVersion.Proposed]) == true)) e.Row.RowError = "Active accounts must have a valid start date."; } Run the program to confirm it works. Make sure the instructor confirms your program works before you leave 17