如何使用Math.js解析器测试MySQL语法

Question

I allow a user to specify a MySQL calculated field in a web form field that might read something like:

(bldgFuelCostElectricity * assetMotorSize) * if(bldgField1>bldgField2,bldgField1-bldgField2,0) * 24

At run time I will substitute other table columns for the camelcase parameters, but before I let the user save this expression as part of a report template, I would like to test the function for validity using Math.js but it doesn't like the IF() construct. Math.js does allow function name overrides, but I cannot make it work with the particular case of IF because that's a reserved word.

How can I test that a MySQL function is valid using Math.js when MySQL has certain functions that already have JavaScript equivalents?

Answer 1

You need to be careful testing MySQL syntax with the parser of math.js, as their syntaxes differ. You will have to define carefully which syntax you support and explicitely test this.

What you can do with math.js is parse expressions into an expression tree and anaylise them. By traversing over the tree, you can validate the syntax. For example:

var node = math.parse('3 * x + 2');
node.traverse(function (node, path, parent) {
  switch (node.type) {
    case 'OperatorNode': console.log(node.type, node.op);    break;
    case 'ConstantNode': console.log(node.type, node.value); break;
    case 'SymbolNode':   console.log(node.type, node.name);  break;
    default:             console.log(node.type);
  }
});
// outputs:
//   OperatorNode +
//   OperatorNode *
//   ConstantNode 3
//   SymbolNode x
//   ConstantNode 2

So in your case, you can just parse your expression and then analyze the returned tree:

var node = math.parse('(bldgFuelCostElectricity * assetMotorSize) * if(bldgField1>bldgField2,bldgField1-bldgField2,0) * 24');
// node.traverse(...)

See docs for more information: http://mathjs.org/docs/expressions/expression_trees.html