Question

I have a query filter written in human readable language. I need to parse it and convert to the SQL where clause. Examples are:

CustomerName Starts With 'J'  

becomes

CustomerName LIKE 'J%' 

and

CustomerName Includes 'Smi' 

becomes

CustomerName LIKE '%Smi%' 

The full expression to be parsed may be much more complicated such as

CustomerName Starts With 'J' AND State = 'CA' 

should become

CustomerName LIKE 'J%' AND State = 'CA' 

What is the best way to go about this? Can it be done easily with RegEx (I am not a regex expert).

Answer 1

In the absence of other answers I’ll chuck in my 2 cents:

It seems to me that you’re actually creating a new language, albeit one that’s very similar to an existing one. So I suspect there are many techniques from the field of computer language interpretation that could make this a simpler task.

The other thing to be cautious of are accidental (or intentional) SQL injection problems.

I’ve not tackled a task like this, but if I were approaching this using Regex I’d be tempted to have a separate method for each new syntax and then pass that input to each of the methods. For example here’s how I might handle the ‘Start With’ syntax.

    public void Main()     {         string input = @'CustomerName Starts With 'J' AND State = 'CA'';          ReplaceStartsWith(ref input);         //...         //ReplaceIncludes(ref input);          Console.WriteLine(input);         //Returns: CustomerName LIKE 'J%' AND State = 'CA'     }      void ReplaceStartsWith(ref string input)     {         input = startsWithRegex.Replace(input, match =>             string.Format('LIKE '{0}%'', match.Groups['literal']));     }      &nbsp;      static RegexOptions commonOptions =         RegexOptions.Compiled |         RegexOptions.ExplicitCapture |         RegexOptions.IgnoreCase |         RegexOptions.IgnorePatternWhitespace |         RegexOptions.Singleline;      &nbsp;      static Regex startsWithRegex = new Regex(         @'\bstarts\s+with\s+'(?<literal>[^']*)''         , commonOptions);