[英]Apply a dynamically-built expression on non-generic DbSet
我有以下情况:
我在编译时有一个未知的DbSet,它是通过其类型获得的,例如:
DbSet entities = _repository.Context.Set(myType)
我有一个给定类型的动态构建的表达式,
Expression myFilter;
//构建为myType
的表达式,在运行时构建
如何将myFilter
应用于entities
,以便基于myFilter
过滤出实体?
以下是可能对您有帮助的代码:它最终创建了一个myType的IQueryable,该IQueryable实际上代表了类似SELECT * FROM YourMappedTable Wed Ed = 1的内容,但当然,您可以使用我为演示目的而构建的表达式表达。
class Program
{
static void Main(string[] args)
{
using (var x = new DB01Entities ())
{
Type myType = typeof(Angajati);
var setMethod = typeof(DB01Entities).GetMethods(System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.Public).Where (a => a.Name == "Set" && a.IsGenericMethod).First ().GetGenericMethodDefinition ();
var mySet = setMethod.MakeGenericMethod(myType);
var realSet = mySet.Invoke(x, null);
var param1 = Expression.Parameter(myType, "param1");
var propertyExpresion = Expression.Property(param1, "Id");
var idExpresssion = Expression.Constant(1);
var body = Expression.Equal(propertyExpresion, idExpresssion);
var lambda = Expression.Lambda(body, param1);
var genericTypeCaster = typeof(Program).GetMethod("Caster", System.Reflection.BindingFlags.Static | System.Reflection.BindingFlags.NonPublic).GetGenericMethodDefinition();
var effectiveMethod = genericTypeCaster.MakeGenericMethod(myType);
var filteredQueryable = effectiveMethod.Invoke(null, new Object[] {realSet, lambda });
}
}
private static IQueryable<T> Caster <T> (DbSet<T> theSet, Expression whereCondition) where T : class
{
return theSet.Where(whereCondition as Expression<Func<T, bool>>);
}
}
因此,上面的“ lambda”变量与“ myFilter”等效。 它必须在运行时
Expression<Func<YourType, bool>>.
而mySet是您的“实体” DbSet。编码愉快!
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