I have a public function that queries against a specific entity. I would like to replicate the function for any table I pass in but don't know how. Here is the working function I want to make dynamic:
public string MaxDepartment()
{
CPLinkEntities _context = new CPLinkEntities();
results = _context.LOG_Departments.Max(t => t.LastUpdated); // hard coded
string hex = BitConverter.ToString(results);
hex = hex.Replace("-", "");
return hex;
}
What I would really like to do here is pass in an entity to query against. All entities have a timestamp. Here is what I envision it would look like but doesn't work:
public string MaxDepartment(CPLinkEntities tableName)
{
var results = tableName.Max(t => t.LastUpdated);
string hex = BitConverter.ToString(results);
hex = hex.Replace("-", "");
return hex;
}
Calling the function from controller then would be:
CPLinkEntities context = new CPLinkEntities();
var tableName = context.LOG_Departments;
var maxDept = cf.MaxDepartment(tableName);
The easiest way to do it without changing any of your existing classes (if you can, see Oleksii's answer ) is to manually create the expression tree and have it select the property you want.
public static string MaxDepartment<U>(IQueryable<U> table)
{
var parameter = Expression.Parameter(typeof(U));
var property = Expression.Property(parameter, "LastUpdated");
var lambada = Expression.Lambda<Func<U, byte[]>>(property, parameter);
var results = table.Max(lambada);
string hex = BitConverter.ToString(results);
hex = hex.Replace("-", "");
return hex;
}
You would call it via
using(CPLinkEntities _context = new CPLinkEntities()) //You forgot to dispose in your original example
{
var max = MaxDepartment(_context.LOG_Departments);
//Do whatever you want with max here.
}
This will fail at runtime if you try to pass in a table that does not have a LastUpdated
property.
I think you should mark your entity with an interface like this:
public interface ILastUpdatable
{
byte[] LastUpdated {get;set;}
}
public partial class LOG_Departments : ILastUpdatable
{
}
and then make your method expecting an object of type that implements an interface like this:
public string MaxDepartment<TLastUpdatable>(IQueryable<TLastUpdatable> updatables)
where TLastUpdatable : class, ILastUpdatable
{
var results = updatables.Max(t => t.LastUpdated);
string hex = BitConverter.ToString(results);
hex = hex.Replace("-", "");
return hex;
}
UPDATE: Also you would consider to use it as extension method:
public static class MaxUpdatableExtensions
{
public static string MaxDepartment<TLastUpdatable>(this IQueryable<TLastUpdatable> updatables)
where TLastUpdatable : class, ILastUpdatable
{
var results = updatables.Max(t => t.LastUpdated);
string hex = BitConverter.ToString(results);
hex = hex.Replace("-", "");
return hex;
}
}
and call it like this:
CPLinkEntities _context = new CPLinkEntities();
var results = _context.LOG_Departments.MaxDepartment();
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.