E 'possibile ??
Sì, lo è.
primo luogo, alcuni aiutanti:
using System;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
namespace YourNamespace
{
internal static class DbHelpers
{
public static object GetColumnById(this object dbContext, string tableName, string columnName, object id)
{
var table = (IQueryable)dbContext.GetType().GetProperty(tableName).GetValue(dbContext, null);
var row = Expression.Parameter(table.ElementType, "row");
var filter = Expression.Lambda(Expression.Equal(Expression.Property(row, "Id"), Expression.Constant(id)), row);
var column = Expression.Property(row, columnName);
var selector = Expression.Lambda(column, row);
var query = Call(Where.MakeGenericMethod(row.Type), table, filter);
query = Call(Select.MakeGenericMethod(row.Type, column.Type), query, selector);
var value = Call(FirstOrDefault.MakeGenericMethod(column.Type), query);
return value;
}
private static readonly MethodInfo Select = GetGenericMethodDefinition<
Func<IQueryable<object>, Expression<Func<object, object>>, IQueryable<object>>>((source, selector) =>
Queryable.Select(source, selector));
private static readonly MethodInfo Where = GetGenericMethodDefinition<
Func<IQueryable<object>, Expression<Func<object, bool>>, object>>((source, predicate) =>
Queryable.Where(source, predicate));
private static readonly MethodInfo FirstOrDefault = GetGenericMethodDefinition<
Func<IQueryable<object>, object>>(source =>
Queryable.FirstOrDefault(source));
private static MethodInfo GetGenericMethodDefinition<TDelegate>(Expression<TDelegate> e)
{
return ((MethodCallExpression)e.Body).Method.GetGenericMethodDefinition();
}
private static object Call(MethodInfo method, params object[] parameters)
{
return method.Invoke(null, parameters);
}
}
}
ed ora la vostra funzione:
public string Get_Field_By_Id(string table_Name, string field_Name, string PK_val)
{
using (var db = new mydbcontext())
return Convert.ToString(db.GetColumnById(table_Name, field_Name, PK_val));
}
fonte
2015-09-01 00:13:09
bene se avete bisogno di questo tipo di funzionalità la prima cosa nella mente è la riflessione (ma non all'interno IQueryable) : var tableItem = db.table_Name.Where (p => p.Id = PK_val) .FirstOrDefault(); var x = tableItem.GetType(). GetProperty (FieldName) .GetValue (tabelItem, null); – Den
hai considerato l'utilizzo del pattern di repository? – Arash
@Arashjo no, puoi mostrarmi la via, fare una risposta ?? –