GetExpression Method C# with Example

public static Expression> GetExpression(IList filters) 
{ 
Expression exp = null; 
// Represents a named parameter expression. {parm => parm.Name.Equals()}, it is the param part 
// To create a ParameterExpression need the type of the entity that the query is against an a 
name 
// The type is possible to find with the generic T and the name is fixed parm 
ParameterExpression param = Expression.Parameter(typeof(T), "parm"); 
// It is good parctice never trust in the client, so it is wise to validate. 
if (filters.Count == 0) 
return null; 
// The expression creation differ if there is one, two or more filters. 
if (filters.Count != 1) 
{ 
 

if (filters.Count == 2) 
// It is result from direct call. 
// For simplicity sake the private overloads will be explained in another example. 
exp = GetExpression(param, filters[0], filters[1]); 
else 
{ 
// As there is no method for more than two filters, 
// I iterate through all the filters and put I in the query two at a time 
while (filters.Count > 0) 
{ 
// Retrieve the first two filters 
var f1 = filters[0]; 
var f2 = filters[1]; 
//  To  build  a  expression  with  a  conditional  AND  operation  that  evaluates 
// the second operand only if the first operand evaluates to true. 
// It needed to use the BinaryExpression a Expression derived class 
// That has the AndAlso method that join two expression together 
exp = exp == null ? GetExpression(param, filters[0], filters[1]) : 
Expression.AndAlso(exp, GetExpression(param, filters[0], filters[1])); 
// Remove the two just used filters, for the method in the next iteration finds the 
next filters 
filters.Remove(f1); 
filters.Remove(f2); 
// If it is that last filter, add the last one and remove it 
if (filters.Count == 1) 
{ 
exp = Expression.AndAlso(exp, GetExpression(param, filters[0])); 
filters.RemoveAt(0); 
} 
} 
} 
} 
else 
// It is result from direct call. 
exp = GetExpression(param, filters[0]); 
// converts the Expression into Lambda and retuns the query 
return Expression.Lambda>(exp, param); 
}