Delphi Programming

TLocateOptions Type

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Definition (Delphi 6, 2010):

TLocateOptions = set of TLocateOption;

TLocateOptions is a set of TLocateOption.

Locate options are used to control how the TDataset Locate method matches it's results. The two options are:

  • loCaseInsensitive: Matching does not take case-sensitivity into account.
  • loPartialKey: Looks at only part of the database field to match data i.e. looking for "SMO" with this option would return a match for "SMOKED HADDOCK" or SMOTE" or "SMOULDER".

Technical CommentsEdit

Locate is used to search a dataset (such as a TTable or a TQuery) for a record that corresponds to certain conditions. It returns True if it finds a matching record, and it makes that record the "current" record. Otherwise it returns False.

Delphi's help gives the following syntax for Locate:

function Locate(const KeyFields: string; const KeyValues: Variant; Options: TLocateOptions): Boolean;

KeyFields is a string, containing one field n ame or several field names separated by semicolons.

Suppose that we have a table Products.DB with the following fields:

id   - alfanumeric - size 2 code - alfanumeric - size 2 size - integer KeyFields could be 'id' or 'id;code' or 'id;code;size'.

KeyValues is a "variant", containing the value(s) to search for. A variant can be of any type: string, integer, boolean,...

If there is only one field in KeyFields, then KeyValues simply contains the value to search for. Examples:

  Found := Product.Locate('id', '12', []);   Found := Product.Locate('size', 3,  []); If there are several fields in KeyFields, then KeyValues should be a "variant array". It is allowed to construct that variant array "on the fly" using the VarArrayOf function. Example:

  Product.Locate('id;code', VarArrayOf(['12', 'AB']), []); Options is a "set" that optionally specifies additional search conditions when your condition contains one or more *string* fields: - if Options contains "loCaseInsensitive", then there is no difference between upper case and lower case; - if Options contains "loPartialKey", then also *partial* matches for string fields are located; - if Options is empty, or if KeyFields does not include any string fields, Options is ignored.


To search for all products with an 'id' starting with '2':

  Found := Product.Locate('id',   '2', [loPartialKey]);  

  To search for all products with a 'code' starting with 'a' or 'A':

  Found := Product.Locate('code',   'a', [loCaseInsensitive, loPartialKey]);


[] or [loCaseInsensitive] or [loPartialKey] or [loCaseInsensitive, loPartialKey] :)

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