Home > Articles

This chapter is from the book

3.3 Locate Records with the DataTable Object

Using the DataTable object, you can use another object called the DataRow object that allows you to locate a specific row in the data table. This is useful when you want to present your users with a search mechanism for your form. This How-To shows you how to locate a specific row within your data table and how to use the same data table for two different purposes.

After you have your DataTable object loaded in memory, you want to be able to locate specific records within the DataTable object. How do you locate records in the DataTable object?

Technique

For this How-To, you are going to use a ComboBox control instead of a ListBox control. You will use the same technique for loading the combo box as you would the list box. The change comes when you select an item from the combo box.

When an item is selected in the combo box, the SelectedIndexChanged event is fired off. Within this event, you will take the combo box's SelectedItem, which gives the ValueMember that is located in the selected row, and use that with the Find method off the DataTables Rows collection.

With the data row located, the corresponding columns are loaded into text boxes on the form, as shown in Figure 3.4.

Figure 3.4 This combo box will point the user to a specific customer.

Steps

Open and run the VB.NET—Chapter 3 solution. From the main form, click on the command button with the caption How-To 3.3. When the form loads, pick a new customer from the list that is presented in the customer ComboBox control. You will see the text boxes below the ComboBox control display new data that corresponds to the chosen customer.

  1. Create a new Windows Form.

  2. Add some labels, combo boxes, and text boxes, as listed in Table 3.4.

Table 3.4 Label, TextBox, and ComboBox Control Property Settings

Object

Property

Setting

Label

Name

Label1

Caption

Customer

ComboBox

Name

cboCustomers

Label

Name

Label2

Caption

Customer ID

Label

Name

Label3

Caption

Company Name

Label

Name

Label4

Caption

Address

Label

Name

Label5

Caption

City

TextBox

Name

txtCustomerID

TextBox

Name

txtCompanyName

TextBox

Name

txtAddress

TextBox

Name

txtCity


You will also want to make sure that the Text properties in the TextBox controls are blank.

  1. In the class module for the form, add the following two Private declarations just below the line of code that reads Windows Form Designer generated code.

    Private modaCust As OleDb.OleDbDataAdapter
    Private mdtCust As DataTable = New DataTable()

    These lines of code declare a data adapter and a data table that will be used throughout the form.

NOTE

Adding the m on the front tells you that it is a module- or member-level variable.

Also, remember that although you are declaring this at the form level, the connection that is used for the data adapter is not going to be left open the whole time the form is. When the data table is filled, the connection is opened. Then the data is accessed locally using XML under the covers. It is disconnected from the server.

  1. Add the code shown in Listing 3.4 to the Load event of the form. Almost identical to the code in the last How-To to load a ListBox control, this code sets modaCust to a SQL String and the connection string to be used. mdtCust is then filled using the Fill method of modaCust. Next, the first element in the DataColumn array called dc is set to the CustomerID column. mdtCustPrimaryKey is then set to the DataColumn array. Last, the DataSource, DisplayMember, and ValueMember properties are set.

Listing 3.4 frmHowTo3_3.vb: Loading a ComboBox by Using the DataTable Object

Private Sub frmHowTo3_3_Load(ByVal sender As Object, _
        ByVal e As System.EventArgs) Handles MyBase.Load

    Dim strSQL As String
    Dim dc(1) As DataColumn

    '-- Set up the exception catch
    Try

      '-- Create the data adapter and fill the data table
      modaCust = New _
         OleDb.OleDbDataAdapter("Select * From Customers", _
(BuildCnnStr("(local)", "Northwind")))
      modaCust.Fill(mdtCust)

      '-- Set up the primary key for the data table
      dc(0) = mdtCust.Columns("CustomerID")
      mdtCust.PrimaryKey = dc

      '-- Bind the data to the combo box
      cboCustomers.DataSource = mdtCust
      cboCustomers.DisplayMember = "CompanyName"
      cboCustomers.ValueMember = "CustomerID"


    Catch oexpData As OleDb.OleDbException
      MsgBox(oexpData.Message)
    End Try

  End Sub

The PrimaryKey property that was set will be used in the code for the next step by the Find method of mdtCust's Rows collection.

  1. This last bit of code needs to be added to the SelectedIndexChanged event of the cboCustomers ComboBox control. As with the last step, when a data column was set up for the PrimaryKey property, in this step an array is specified to pass the SelectedItem value to find the Find method. The text boxes' Text properties are then set to the column values by using the ToString method.

Listing 3.5 frmHowTo3_3.vb: Locating a Record in the Data Table, and Then Assigning Values to Text Boxes

Private Sub cboCustomers_SelectedIndexChanged(ByVal sender As System.Object, _
          ByVal e As System.EventArgs) _
Handles cboCustomers.SelectedIndexChanged

    Dim drCurr As DataRow
    Dim aFindValue(0) As Object

    '-- Load the item to look up, and use the find method
    aFindValue(0) = cboCustomers.SelectedItem(0)
    drCurr = mdtCust.Rows.Find(aFindValue)

    '-- Load up the fields on the form
    txtCustomerID.Text = drCurr("CustomerID").ToString
    txtCompanyName.Text = drCurr("CompanyName").ToString
    txtAddress.Text = drCurr("Address").ToString
    txtCity.Text = drCurr("City").ToString

  End Sub

How It Works

When a user picks a customer from the cboCustomer ComboBox control, the code then locates the desired value within the mdtCust data Table using the Find method off the rows collection. Text boxes are then loaded from the row that is retrieved.

Comments

Locating records within a data table and data row is pretty easy when you're using the methods that are supplied. ADO.NET provides the control you need, not only at the overall hierarchical level, but also at the row and column levels.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020