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C++Builder Database Architecture
Locate
The Locate method takes three parameters: a string that identifies the field(s) you want to
search, a variant that lists the values to search for, and a TLocateOptions set variable that
specifies options for the search. Here’s the syntax for the Locate function:
System::Boolean __fastcall Locate(const System::AnsiString KeyFields,
const System::Variant &KeyValues, TlocateOptions Options);
You separate multiple field names with semicolons in Locate’s KeyFields parameter and pass
their values as a variant array in its KeyValues parameter. Locate’s Options parameter is of type
TLocateOptions and enables you to specify options that control the search. The parameter is
a set variable and can have two possible values, loCaseInsensitive and loPartialKey. The
first option, loCaseInsensitive, tells Locate to perform a search that is not case sensitive. The
second one, loPartialKey, allows for partial key searches. You can pass either one or both of
these by assigning them to a set variable like so:
TLocateOptions SearchOpts
SearchOpts Locate(“NAME”,”Cri”,SearchOpts);
Locate uses the fastest available means of satisfying your search criteria. If an index exists that
can satisfy the search request, Locate uses it. If an index does not exist that can service the
search, a BDE filter is constructed. Either way, the fastest possible path to your data is taken.
Locate returns true if it’s able to locate the data you request, and false if it isn’t.
Lookup
Similarly to the Locate function, the Lookup function takes three parameters: a string
parameter specifying a semicolon-delimited list of columns to search for, a variant or variant
array specifying the column values to search for, and a string parameter listing the names of
columns to return in the function’s result. Here’s the syntax for the Lookup function:
System::Boolean __fastcall Lookup(const System::AnsiString KeyFields,
const System::Variant &KeyValues,const System::AnsiString ResultFields);
In addition to performing a TDataset search, Lookup returns values from the operation as well.
If a matching row cannot be found, Lookup returns a null variant. If a matching row is found,
Lookup first processes any lookup fields you’ve defined for its associated TDataset, and then
returns the values of the fields you’ve specified in ResultColumns. If ResultColumns lists
multiple fields, the result is a variant array; otherwise, it’s just a simple variant.
Cached Updates
C++Builder’s cached updates mechanism enables you to delay applying updates to your
database back end. You can decide when to apply updates, and then apply them all at once.
Normally, updates are applied as soon as you make them. For client/server applications, this
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