The LA Fox Developer Newsletter

VFP Hot Tips...

From TakeNote Computer Consulting

Returning a Value from a Form

A common question we get asked in our VFP training classes is “How do I return a value from a form?” It’s really pretty simple. All you need to do is place

RETURN(THIS.ValueToReturn)

in the UnLoad Event of the form. You need to keep a couple things in mind though.

I .You can’t return the Value property of an object on the form because the Destroy Event for all form objects has already occured. Instead, place the value to be returned in a form property. That way it’ll be in scope when it’s needed. 2.The form’s WindowType property needs to be set to 1-Modal.

Now that we’ve got the form built, we need to know how to call it. Call the form with:

DO FORM ABC TO xyz

where ABC is the form name and xyz is where the value will be
stored. Tha value can be a memory variable or property.

Field Caption Gotcha!

When working with the Table Designer to set field Caption properties, watch out for this little trip-up. If you click on the Expression Builder button to the right of the Caption text box and type a caption *without* quotes, VFP will not consider that a valid expression. If you put it in quotes, he will. The only problem there is that your caption is in quotes everywhere in your app.

Work around: Just type the field captions in and don’t bring up the Expression Builder. When you type them directly in to the Table Designer, they do not require quotes.

The SetAll Method

Do you find yourself setting the same property for multiple items at a time? For example, you decide you want the font for all the header captions in a grid to all be 12 point Anal with a blue background and yellow text. Now you could manually set the Font and FontSize properties in the Form Designer or you could place these 3 lines in the Init event of the grid to have all of those font settings set a runtime.

TH!S.SETALL(”FontName”,”AriaI”,”Header”)

THIS.SETALL(”BackColor”,RGB(O,O,255),”Header’)

THIS.SETALL(”ForeColor”,RGB(255,255,O),”Header”)

(Con’t, page 12)

December 1998

Integers and Other

Strange Animals

At one time or another we all run into the problem of how to uniquely identify records in a table. We all have our favorite schemas for accomplishing this. But in the final analysis using the integer field type for key fields is more often than not the best solution. In this document I will talk about the integer field type and why integers make great keys and indexes and relational database terms as they relate to keys,.

Integers - Not Like in Elementary School

Why is there an integer field type? I mean, an integer is just another numeric with nothing following the decimal point. Isn’t it?

In a word, no.

The data type name “integer” gives the false impression that it holds the kind of information that we learned about oh so many years ago. The integer data type actually holds a base 256 value! This means that using only four characters you can store a integer values from -2GB+1 TO 2GB-I. That’s more than four billion unique values can be stored in a four-byte field. A two- byte field -32K+1 to 32K-I. A one-byte field -127 to +127 including zero. It rapidly becomes clear that using the integer data type for indexing and primary keys is very attractive. In one very compact field you can have one heck of a lot of unique values.

In addition, indexing on the integer field is much faster than indexing on character expressions. Numeric comparisons are faster and easier for FoxPro to perform than character comparisons.

Also the size of the index file is much smaller than indexing on a character field capable of holding the same number of unique values. You will also find that SEEKs and joins are also performs significantly faster.

Relational Database Terminology

In this discussion we will be looking the definitions of some relational database terminology in the context of FoxPro. In most ways these terms are have the same meaning as the pure RDBMS model. But there are some differences.

record of a table that can be used to identify a record.

single field in a table.

Compound/Concatenated key - A key made up of two or more fields in a record to establish uniqueness.

Surrogate Key - A Simple key used to uniquely identify oneand-only-one record in that table. This value has no

(Con’t, page 11)

Page 10