Working with DBLookupComboBox

Working with DBLookupComboBox

The TfrxDBLookupComboBox is the most powerful dialog control but also the most complex.

Setup Requirements

You need:

1. A dataset in your report (on the Data page) with lookup values
2. A DBLookupComboBox on the dialog page
3. Proper configuration of the lookup properties

Step-by-Step Configuration

1. Create the lookup dataset:

On the Data page:
  - Add TfrxFDDatabase (connects to your database)
  - Add TfrxFDQuery named "qryCustomers"
  - SQL: SELECT CustomerID, CompanyName FROM Customers ORDER BY CompanyName
  - Set Active = True (or open it in script)

2. Create a frxDBDataset:

Add TfrxDBDataset:
  Name: dsCustomers
  DataSet: qryCustomers
  UserName: "Customers"

3. Configure the DBLookupComboBox:

Properties:
  Name: DBLookupComboBox1
  ListSource: dsCustomers
  KeyField: "CustomerID"      (the value you want)
  ListField: "CompanyName"    (what the user sees)
  Width: 300

Setting Default Value

In the DialogPage OnShow event:

pascal

procedure DialogPage1OnShow(Sender: TfrxComponent);
var
  ds: TfrxDataSet;
begin
  // Set to first item in list
  ds := DBLookupComboBox1.ListSource.DataSet;
  
  if Assigned(ds) and (ds.RecordCount > 0) then
  begin
    ds.First;
    DBLookupComboBox1.KeyValue := ds.Value[DBLookupComboBox1.KeyField];
  end;
end;

Getting the Selected Value

The selected value is in DBLookupComboBox1.KeyValue:

pascal

// KeyValue contains the CustomerID (the value from KeyField)
// Text contains the CompanyName (the value from ListField)

var
  SelectedID: Integer;
  SelectedName: String;
begin
  SelectedID := DBLookupComboBox1.KeyValue;      // e.g., 123
  SelectedName := DBLookupComboBox1.Text;        // e.g., "Acme Corp"
end;

---

Using Dialog Values in Queries

This is where it gets tricky. The Parameter Editor has limited use with dialog controls.

Method 1: Direct Parameter Assignment (RECOMMENDED)

Set query parameters directly in the dialog’s OnCloseQuery event:

pascal

procedure DialogPage1OnCloseQuery(Sender: TfrxComponent; var CanClose: Boolean);
begin
  // Close the queries first
  qryOrders.Close;
  
  // Set parameter values from dialog controls
  qryOrders.ParamByName('CustomerID').Value := DBLookupComboBox1.KeyValue;
  qryOrders.ParamByName('StartDate').Value := DateEdit1.Date;
  qryOrders.ParamByName('EndDate').Value := DateEdit2.Date;
  qryOrders.ParamByName('Status').Value := ComboBox1.Text;
  
  // Reopen with new parameters
  qryOrders.Open;
end;

Your query SQL:

sql

SELECT * FROM Orders 
WHERE CustomerID = :CustomerID 
  AND OrderDate BETWEEN :StartDate AND :EndDate
  AND Status = :Status
```

**Leave the Parameter Editor values EMPTY** - you're setting them in code.

### Method 2: Using Report Variables (Alternative)

If you prefer using the Parameter Editor, use report variables as an intermediary:

**Step 1: Create variables** (Report → Variables):
```
Variable Name: CustomerID
Type: Integer
Value: 0

Step 2: Set variables in dialog script:

pascal

procedure DialogPage1OnCloseQuery(Sender: TfrxComponent; var CanClose: Boolean);
begin
  Report.Variables['CustomerID'] := Integer(DBLookupComboBox1.KeyValue);
  Report.Variables['StartDate'] := DateEdit1.Date;
end;
```

**Step 3: Use in Parameter Editor:**
```
Parameter: CustomerID
Value: <CustomerID>

Problem with this method: Articles sometimes evaluates variables incorrectly. Method 1 is more reliable.