Teach Yourself Borland C++ in 14 Days - portal

448 Day 12
Operator Use
() Encloses individual elements of a compound expression
[] Encloses field names with spaces
AND, OR, NOT Joins individual elements of compound expressions
You can also filter records using the OnFilterRecord event. OnFilterEvent looks like this:
void __fastcall TForm1::Table1FilterRecord(TDataset *TDataset,
Boolean &Accept)
{
Accept=(dlr==vhlead);
}
The OnFilterRecord event handler sets the value of the Accept parameter to indicate whether
a row meets the filter criteria. Note that the TDataset to which the filter corresponds is also
passed in as a parameter. In the previous example, only those properties with gas heat are
visible when the filter is active. Note the use of the Value variant property to set the Accept
parameter.
You can also use the FindFirst, FindNext, FindPrior, and FindLast methods to search an
unfiltered TDataset using a filter expression. FindFirst locates the first row matching the
filter expression; FindNext locates the next one that does. FindPrior locates the previous row
matching the filter expression, and FindLast locates the last one that does.
FilterOptions is a set variable that can include two possible elements:
Element Meaning
foCaseInsensitive The filter ignores the case of the TDataset’s data
foNoPartialCompare Partial field matches aren’t allowed
You can set them using C++Builder’s Object Inspector.
Ranges
The SetRangeStart, SetRangeEnd, EditRangeStart, EditRangeEnd, ApplyRange, and SetRange
methods also allow you to limit the set of rows visible to your application. Unlike
C++Builder’s more flexible local filters, the rows within the set must correspond to a
consecutive set of keys within an index when you’re dealing with local tables. For SQL tables,
the fields can be any listed in the IndexFieldNames property. The CancelRange method makes
all rows again visible to your application.
Locate/Lookup
The Locate and Lookup methods allow you to search for rows in a table. They’re much more
flexible than the FindKey/SetKey family of functions because they do not require the use of an
index and can therefore be used with Query and StoredProc components in addition to Table
components. You choose the data you want, and the BDE finds the best way to access it.