selec implem

This commit is contained in:
duboissim 2024-03-14 18:32:38 +01:00
parent b100bf03d8
commit d40cbb70df
1 changed files with 41 additions and 74 deletions

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@ -152,10 +152,27 @@ prompt, but which may include selectors. Selectors are terms of the form
*/
delete(Table, Conds) :-
(tabl(Table, _) ->
(rows(tables, Row), \+ (member(Cond, Conds), \+ Cond) -> retract(Row); true);
row(Table, Row),
does_match(Conds, Table, Row)
;
throw("Table doesn't exist")
).
does_match([], _, Row) :- !.
does_match([Cond|Rest], Table, Row) :-
% Extract the operator, field and value from the condition
Cond =.. [Operator | T],
[+F, S] = T,
tabl(Table, Cols),
member(F, Cols),
nth0(Index, Cols, F),
nth0(Index, Row, Value),
apply(Operator, [Value, S]),
does_match(Rest, Table, Row).
:- dynamic selec/4.
/*
Note that the name of this predicate is selec (without t) for the simple
@ -186,86 +203,36 @@ For example:
findall(Values, selec(persons,[+id,+first],[],Values), Projections)
returns: Projections = [[0, "Jeffrey"], [1, "Lorena"], [2, "Joseph"], ...
*/
selec(Table, Selectors, Conds, Projection) :-
selec_help(Table, Selectors,[], [], ColumnNames, ColumnValue),
%remove combinations that don't exist
row(Table, Row),
has_value(ColumnValue, Row),
selec(Table, Selector, Cond, Projection) :-
tabl(Table, Cols),
row(Table, R),
does_match(Cond, Table, R),
selector(R,Cols, Selector, [],[],ColumnNames,ColumnValue),
Projection = ColumnNames/ColumnValue.
%base case
selec_help(_, [], ColumnNames, ColumnValue, ColumnNames, ColumnValue).
selector(_,_,[],ColumnNames, ColumnValue, ColumnNames, ColumnValue):-!.
/**
* Table: name of the table the selection is done one
* Row: A row from the table
* Cols: name of the column of the table
* [Selector|Selectors] name(s) of the column(s) for selection
* AccCols: acumulator list for the column(s) name(s)
* AccVals: acumulator list for the row(s) values
* ColumnNames: List returning the column(s) name(s)
* ColumnValue: List returning the row values for each column
*/
selec_help(Table, [Selector|Selectors], AccCols, AccVals, ColumnNames, ColumnValue) :-
%check if table exist
(tabl(Table, Cols) ->
%check if column exist
member(Selector, Cols) ->
selector(Row, Cols, [+Selector|Selectors], AccCols, AccVals, ColumnNames, ColumnValue):-
(member(Selector, Cols) ->
%find the value corresponding to the column in the row
nth0(Index, Cols, Selector),
row(Table, Row),
nth0(Index, Row, Value),
%go to next column tho evaluate
selec_help(Table, Selectors, [Selector|AccCols], [Value|AccVals], ColumnNames, ColumnValue)
selector(Row, Cols, Selectors, [Selector|AccCols], [Value|AccVals], ColumnNames, ColumnValue)
;
string_concat(Selector, " isn't a column of table ", X),
string_concat(X, Table, Error),
throw(Error)
;
string_concat(Table, " doesn't exist.", Error), throw(Error)
).
/*
Check if a list has all the values in [Value|Rest]
*/
has_value([], _) :- !.
has_value([Value|Rest], List) :-
memberchk(Value, List),
has_value(Rest, List).
evaluate_condition_string(ConditionString) :-
atom_codes(AtomCondition, ConditionString), % Convert string to atom
read_term_from_codes(AtomCondition, Term, []), % Parse the term
call(Term). % Evaluate the parsed term
selec_column(Table, Column, Proj) :-
tabl(Table, Cols),
row(Table, Row),
nth0(I, Cols, Column),
nth0(I, Row, Value),
Proj = Value.
apply_cond(Table, Cond, Proj) :-
tabl(Table, Cols),
row(Table, Row),
nth0(I, Cols, Column),
nth0(I, Row, Value),
split_string(Cond, " ", "", SubStrings),
Decomp = SubStrings,
Decomp = [Column, Op, Value],
check_condition(Column, Op, Value),
Proj = Row.
check_condition(Left, =, Right) :-
Left =:= Right.
check_condition(Left, <, Right) :-
Left < Right.
check_condition(Left, >, Right) :-
Left > Right.
check_condition(Left, <=, Right) :-
Left =< Right.
check_condition(Left, >=, Right) :-
Left >= Right.
check_condition(Left, \=, Right) :-
Left =\= Right.
:- dynamic selec/3.
/*