GetExpression Private overload C# with Example



GetExpression Private overload C# with Example

For one filter: 
Here is where the query is created, it receives a expression parameter and a filter. 
private static Expression GetExpression(ParameterExpression param, QueryFilter queryFilter) 
{ 
// Represents accessing a field or property, so here we are accessing for example: 
// the property "Name" of the entity 
MemberExpression member = Expression.Property(param, queryFilter.PropertyName); 
//Represents an expression that has a constant value, so here we are accessing for example: 
// the values of the Property "Name". 
// Also for clarity sake the GetConstant will be explained in another example. 
ConstantExpression constant = GetConstant(member.Type, queryFilter.Value); 
// With these two, now I can build the expression 
 

// every operator has it one way to call, so the switch will do. 
switch (queryFilter.Operator) 
{ 
case Operator.Equals: 
return Expression.Equal(member, constant); 
case Operator.Contains: 
return Expression.Call(member, ContainsMethod, constant); 
case Operator.GreaterThan: 
return Expression.GreaterThan(member, constant); 
case Operator.GreaterThanOrEqual: 
return Expression.GreaterThanOrEqual(member, constant); 
case Operator.LessThan: 
return Expression.LessThan(member, constant); 
case Operator.LessThanOrEqualTo: 
return Expression.LessThanOrEqual(member, constant); 
case Operator.StartsWith: 
return Expression.Call(member, StartsWithMethod, constant); 
case Operator.EndsWith: 
return Expression.Call(member, EndsWithMethod, constant); 
} 
return null; 
} 
For two filters: 
It returns the BinaryExpresion instance instead of the simple Expression. 
private static BinaryExpression GetExpression(ParameterExpression param, QueryFilter filter1, 
QueryFilter filter2) 
{ 
// Built two separated expression and join them after. 
Expression result1 = GetExpression(param, filter1); 
Expression result2 = GetExpression(param, filter2); 
return Expression.AndAlso(result1, result2); 
} 

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