Incrementally building a query C# with Example

Because LINQ uses deferred execution, we can have a query object that doesn't actually contain the values, but 
will return the values when evaluated. We can thus dynamically build the query based on our control flow, and 
evaluate it once we are finished: 
IEnumerable BuildQuery(int vehicleType, SearchModel search, int start = 1, int count 
= -1) { 
IEnumerable query = _entities.Vehicles 
.Where(x => x.Active && x.Type == vehicleType) 
.Select(x => new VehicleModel { 
Id = v.Id, 
Year = v.Year, 
Class = v.Class, 
Make = v.Make, 
Model = v.Model, 
Cylinders = v.Cylinders ?? 0 
}); 
We can conditionally apply filters: 
if (!search.Years.Contains("all", StringComparer.OrdinalIgnoreCase)) 
query = query.Where(v => search.Years.Contains(v.Year)); 
if (!search.Makes.Contains("all", StringComparer.OrdinalIgnoreCase)) { 
query = query.Where(v => search.Makes.Contains(v.Make)); 
} 
if (!search.Models.Contains("all", StringComparer.OrdinalIgnoreCase)) { 
query = query.Where(v => search.Models.Contains(v.Model)); 
} 
if (!search.Cylinders.Equals("all", StringComparer.OrdinalIgnoreCase)) { 
decimal minCylinders = 0; 
decimal maxCylinders = 0; 
switch (search.Cylinders) { 
case "2-4": 
maxCylinders = 4; 
break; 
 

case "5-6": 
minCylinders = 5; 
maxCylinders = 6; 
break; 
case "8": 
minCylinders = 8; 
maxCylinders = 8; 
break; 
case "10+": 
minCylinders = 10; 
break; 
} 
if (minCylinders > 0) { 
query = query.Where(v => v.Cylinders >= minCylinders); 
} 
if (maxCylinders > 0) { 
query = query.Where(v => v.Cylinders <= maxCylinders); 
} 
} 
We can add a sort order to the query based on a condition: 
switch (search.SortingColumn.ToLower()) { 
case "make_model": 
query = query.OrderBy(v => v.Make).ThenBy(v => v.Model); 
break; 
case "year": 
query = query.OrderBy(v => v.Year); 
break; 
case "engine_size": 
query = query.OrderBy(v => v.EngineSize).ThenBy(v => v.Cylinders); 
break; 
default: 
query = query.OrderBy(v => v.Year); //The default sorting. 
} 
Our query can be defined to start from a given point: 
query = query.Skip(start - 1); 
and defined to return a specific number of records: 
if (count > -1) { 
query = query.Take(count); 
} 
return query; 
} 
Once we have the query object, we can evaluate the results with a foreach loop, or one of the LINQ methods that 
returns a set of values, such as ToList or ToArray: 
SearchModel sm; 
// populate the search model here 
// ... 
List list = BuildQuery(5, sm).ToList();