Expression Builder

Finding the Expression Builder

You can access the Expression Builder in a number of ways. From the Control Panel you can find it by first opening a Form, Browse, or Set. Go to Query at the top of the screen and select Query by Expression from the drop down menu. Alternatively, click the Query by Expression button in the toolbar at the top of the screen.

In either case, the Query by Expression dialog will open. Click the Expression Builder button to the right of either the Filter Expression or Order Expression text boxes to open the Expression Builder. From the Web Project Control Panel you can find the Expression Builder in the Grid Builder. Click the Create a new grid Component button and click OK on the Select Grid Component Template dialog. The Grid Builder will open, on the Design page menu under Grid click on the Data Source link and on the Data Source page and select .dbf Tables. Go back to the Design page menu and under Grid click on Query(DBF). To the right of the filter text box click the Expression Builder button to open the Expression Builder. Note, you can not access the Expression Builder through the Query(AlphaDAO) page. SQL relies more heavily on expressions built through arguments than do .dbf files, which leans more on variables.

The Expression Builder automatically evaluates every expression and displays the value and data type of the result. This prevents you from trying to use an invalid expression. You can see the Result and Type for the current expression displayed in the lower middle portion of the dialog. This works even if there is only one entry in the builder. For Example, if there is a report on field that has a value of the number 12, you will see Result: 12, Type: N appear in the Expression Builder. Type abbreviations for Xbasic include N (Numeric), C (Character), D (Date), L (Logical), P (Pointer), T (Time), B (Blob), U (Collection), A (Any type), Integer (32 bit integer), Short (16 bit integer), {YourType} (A user defined type)

Auto Complete

The Expression Builder uses "auto-complete" technology to help you write functions. The Bubble Help shows a list of functions that start with the letters you type. As you type more letters, the list of possible functions gets narrowed down. The Expression Builder shows the syntax for each function and prompts you for each of the function arguments. Functions are color coded so that the expressions they are placed in are easier to read. Auto-complete feature helps with the syntax of Xbasic functions.

Using Fields in Expressions

The Expression Builder makes it easy to insert different fields into an expression, simply hit F2 to open the Select Field dialog and click on the field you want to insert. Once a field is inside an expression, you can then evaluate that expression's Result and Type. If the inserted field contains multiple records you can use the navigational buttons to move between and evaluate each record individually.

• First

  Evaluates the first record in a given field in an expression

  

• Previous

  Evaluate the expression for the previous record.

  

• Next

  Evaluates the expression for the next record in a given field

  

• Last

  Evaluates the expression for the last record in a field.

  

The current record number being evaluated is displayed below the navigational buttons next to the Record: button. If you click the 'Record:' button you will open the Record Number dialog. If there is a specific record number you want to evaluate, you can type that number into the 'Evaluate Expression for Record Number' textbox and the Expression Builder will evaluate that record. Skip to any record in a field:

Using Functions in Expressions

You can insert functions into expressions. As noted earlier, there is also an auto complete for functions.

Using Arguments in Expressions

If you are working with .dbf files you can create arguments using the Define Arguments dialog. Once you have defined an argument you can then use it in the Expression Builder. Used in conjunction with the fields in your grid this can be quite powerful.

Using Variables

The available categories will depend on the context in which the expression builder is invoked. However, all contexts will have these contexts: Global and Session. A global variable is visible throughout Alpha Anywhere. For example, if the variable is defined by a script in one form, then any other form in your Alpha Anywhere session has access to that variable. A session variable is visible throughout an Alpha Anywhere session. A session is created when you open a new window in Alpha Anywhere (e.g. a new form, or browse window). All scripts on a form, for example, have access to a session variable. If you swap the layout displayed in a window (for example, by pressing the F8 key while viewing a form, to switch to a browse view), session variables remain visible to the new layout displayed in the window (because it is still the same session). If the Expression Builder is invoked from within a Layout, then the Layout category is available. A Layout variable is visible to all scripts and expressions in a form, but if the Layout in the window is swapped (for example, by opening a new form in the same window, or switching to a browse view), then the Layout variables are no longer available. Select Variable dialog:

You can insert system fields into your expressions by hitting the F7 key and selecting a field from the System Fields dialog. System fields include Date, Unbound, Page Number, Page x of y, Page Count, Current Order, Current Filter, Layout Name, and Data Source. Date allows you to insert the current date into an expression. Unbound means there is no field associated with it. Data Source will insert the file path of the current table into your expression. The System Fields Dialog:

Using the Expression Library

The Expression Library lets you store expressions. If you complete an expression that might have current or future use, click the 'Add Expression to Library' button twice to add it to a library.

The 'Add Entry to Expression Library' dialog will open and ask you to name your expression. It will also ask you to select one of three libraries for the expression to live in. The options are the Current Table/Set, the Current Workspace, or the Global Library. This is mainly a question of whether you want your entry to be viewed from other Tables and or Sets in your Workspace, or not, or if you want your expression to be visible from all of your workspaces.

Object Properties

"Object Properties" appear in appropriate contexts in Desktop workspaces. You will not see or use these properties in the Grid Builder or the Web Project Control Panel, only in the Control Panel. If you are building a calculation value expression for a form or a browse layout, or are defining an expression in Action Scripting for an action that is bound to an event on a form or a browse, the Object Properties category will allow you to refer to any property of any object on the layout.