private QueryTokens tokenizeQuery(string query)
{
string[] tokens = query.Split(" ");
QueryTokens queryTokens = new QueryTokens();
foreach (var item in tokens)
{
if (clausesArray.Contains(item))
{
queryTokens.clauses.Add(item);
continue;
}
if (operatorsArray.Contains(item))
{
queryTokens.operators.Add(item);
continue;
}
queryTokens.operands.Add(item);
}
int totalClauses = queryTokens.clauses.Count;
int totalOperators = queryTokens.operators.Count;
int totalOperands = queryTokens.operands.Count;
return(queryTokens);
}
public Expression <Func <User, bool> > buildQuery(string query)
{
QueryTokens tokens = this.tokenizeQuery(query);
string[] operands = tokens.operands.ToArray();
string[] operators = tokens.operators.ToArray();
string[] clauses = tokens.clauses.ToArray();
Expression finalExpression = null;
int operatorIndex = 0;
List <Expression> expressionList = new List <Expression>();
var parameter = Expression.Parameter(typeof(User), "u");
for (int i = 0; i < operands.Length; i += 2)
{
var memberExpression = Expression.Property(parameter, operands[i]);
var isConstantNumeric = int.TryParse(operands[i + 1], out int number);
Expression constant = null;
if (isConstantNumeric)
{
constant = Expression.Constant(number, typeof(int));
}
else
{
constant = Expression.Constant(operands[i + 1]);
}
BinaryExpression expressionBody = null;
switch (operators[operatorIndex])
{
case EQUALS:
expressionBody = Expression.Equal(memberExpression, constant);
break;
case GREATER_THAN:
expressionBody = Expression.GreaterThan(memberExpression, constant);
break;
case GREATER_THAN_EQUAL:
expressionBody = Expression.GreaterThanOrEqual(memberExpression, constant);
break;
case LESS_THAN:
expressionBody = Expression.LessThan(memberExpression, constant);
break;
case LESS_THAN_EQUAL:
expressionBody = Expression.LessThanOrEqual(memberExpression, constant);
break;
default:
Console.WriteLine("Undefined condition encountered. Malformed query");
break;
}
expressionList.Add(expressionBody);
++operatorIndex;
}
if (clauses.Length > 0)
{
for (int i = 0; i < clauses.Length; i++)
{
switch (clauses[i])
{
case AND_CLAUSE:
if (finalExpression == null)
{
finalExpression = Expression.AndAlso(expressionList[i], expressionList[i + 1]);
}
else
{
finalExpression = Expression.AndAlso(finalExpression, expressionList[i + 1]);
}
break;
case OR_CLAUSE:
if (finalExpression == null)
{
finalExpression = Expression.OrElse(expressionList[i], expressionList[i + 1]);
}
else
{
finalExpression = Expression.OrElse(finalExpression, expressionList[i + 1]);
}
break;
default:
Console.WriteLine("Unwanted clause encountered. Malformed query");
break;
}
}
var userExpressionTree = Expression.Lambda <Func <User, bool> >(finalExpression, new[] { parameter });
return(userExpressionTree);
}
else
{
// No clause exists, thus we will return only one expression
var userExpressionTree = Expression.Lambda <Func <User, bool> >(expressionList[0], new[] { parameter });
return(userExpressionTree);
}
}