selec implem

solution.pl

@@ -151,10 +151,27 @@ prompt, but which may include selectors. Selectors are terms of the form
 (See tests.pl for some concrete usage examples.)
 */
 delete(Table, Conds) :- 
-	(tabl(Table, _) ->
-		(rows(tables, Row), \+ (member(Cond, Conds), \+ Cond) -> retract(Row); true);
-		throw("Table doesn't exist")
-	).
+    (tabl(Table, _) ->
+        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.
 /*
@@ -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),
-    Projection = ColumnNames/ColumnValue.
+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) ->
-			%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)
-    	;   
-			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)
+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),
+        nth0(Index, Row, Value),
+		%go to next column tho evaluate
+        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)
     ).
-/*
-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.
 /*