How can I write boolean predicates in XPath?-CodePudding

I develop a CAD program and I would like to create smart selection operation. The user could formulate search phrases to select/deselect elements in the project. I thought if I build an XML DOM for the elements in the project and I call xpath searches against the DOM to get the list of the matching elements in the project could work.

If I have an Element type with three fields and stored in XML as attr1, attr2, attr3 attributes as Element tags:

<Elements>
  <Element attr1="" attr2="" att3="">
  ...
  <Element attr1="" attr2="" att3="">
</Elements>

How can I write an XPath equals to the following:

( attr1="value1" AND attr2="value2" ) OR attr3="value3"

Or here is another phrase just because you could not say : because of the operation priorities the parentheses are not necessary!

( attr1="value1" OR attr2="value2" ) AND attr3="value3"

I couldn't find anything about the usage of parenthesis in xpath on W3Schools. The call of the IXMLDocument calls are not necessary just the xpath phrases (if possible = there are parenthesis in XPath).

Or I have to do the logical operations on SearchNodes result lists manually?

CodePudding user response：

Your logical criteria of elements of interest, presented in an ad hoc syntax,

( attr1="value1" AND attr2="value2" ) OR attr3="value3"

corresponds to this XPath,

//*[( @attr1="value1" and @attr2="value2" ) or @attr3="value3"]

and will select all elements, regardless of name, that have the listed attribute values that meet the boolean expression in the predicate ([...]).

Replace * with Element to select only those elements named, Element, that meet the criteria.

CodePudding user response：

In what cases you need parenthesis or not is specified at w3.org. There the operator precedence of XPath is specified.

[...] normatively defines built-in precedence among the operators of XPath.

#   Operator                        Associativity  
1   , (comma)                       either  
2   for, let, some, every, if       NA
3   or                              either
4   and                             either
5   eq, ne, lt, le, gt, ge, =, 
    !=, <, <=, >, >=, is, <<, >>    NA
6   ||                              left-to-right
7   to                              NA
8    , - (binary)                   left-to-right
9   *, div, idiv, mod               left-to-right
10  union, |                        either
11  intersect, except               left-to-right
12  instance of                     NA
13  treat as                        NA
14  castable as                     NA
15  cast as                         NA
16  =>                              left-to-right
17  -,   (unary)                    right-to-left
18  !                               left-to-right
19  /, //                           left-to-right
20  [ ], ?                          left-to-right
21  ? (unary)                       NA