Hi Joao,

>I'm a biginner in VFP, i understand what you said, but when a open the rule that comes with Expression builder and i don't now what i do.

What you do is store it in a procedure or class method then do in the Rule:

IsKeyUnique(tcTheTableName, tcNameField, teValue, tiPK)

With data this may look like:

IsKeyUnique("clientes", "c_codigo", c_codigo, id_PK)

This will fire anytime the field is changed, if you want to validate it just when you put it in the textbox (easier!), put this in the Valid() event of your textbox and forget about the DataBase rule:

local lnCurWA, llReturn, lcExact, leValue, liPK

with This
	lnCurWA = select()
	lcExact = set('exact')
	set exact on
	lcPrimaryKey = dbgetprop(juststem(dbf(juststem(.ControlSource))),'table','PrimaryKey')
	liPK = eval(forceext(.ControlSource, lcPrimaryKey))

	use (dbf(juststem(.ControlSource))) again alias EnforceUnique in 0
	select EnforceUnique

	llReturn = !seek(.Value, 'enforceunique', justext(.ControlSource)) or eval(lcPrimaryKey) = liPK

	use
	select (lnCurWA)
	set exact &lcExact

endwith
if !llreturn
	MessageB('Value is not unique')
endif
return iif(llReturn, .T., 0)