위의 답 중 아무 것도 처리하지 않는 것 (즉, 반환 된 열만 필터링하여 기본 형식 열에 만 사용하고 파생 형식 정보가있는 행은 필터링하지 않는다는 질문에 대답하기 위해) 익명 형식으로이 작업을 수행하는 방법은 매우 간단합니다. 세부 사항을 다루는 또 다른 stackoverflow 질문은 here을 참조하십시오.
db.BaseTypes.Select(o => new { Prop1 = o.Prop1, Prop2 = o.Prop2, ....})
.AsEnumerable()
.Select(a => new BaseType() { Prop1 = a.Prop1, Prop2 = a.Prop2, ...});
는 엔티티 Linq에 -에 - 익명 개체의 목록을 반환 할 것, 다시 Linq에 - 투 - 객체에 .AsEnumerable()
반환을하고 당신을 수 있지만 :
아이디어는 이런 일을하는 것입니다 new BaseType()
에 개체 이니셜 라이저 목록을 호출하십시오.
이것은 유형에 특정한 불행한 단점이 있습니다. 여기 사무실에있는 누군가는 일반적인 것을 쓰고 싶습니다. 그래서 저는 곧 돌아올 것이고이 대답을 완전히 일반적인 버전으로 편집 할 것입니다.
EDIT (하지만 생산 EntityFramework에서 테스트) 다음 SELECTDYNAMIC 코드 this answer에
감사합니다.
public static class QueryableExtensions {
/// <summary>
/// Constructs a query that only selects the columns that are actually in the type <typeparamref name="T"/> as public properties.
///
/// Useful for inherited types when you only want the base type information.
/// </summary>
/// <remarks>
/// This function materializes the query. You'll want to call the where clauses BEFORE this call (since it is an optimization).
/// </remarks>
/// <typeparam name="T">Entity type.</typeparam>
/// <param name="query">Source query.</param>
/// <returns>An IEnumerable of items of type <typeparamref name="T"/>.</returns>
public static IEnumerable<T> FilterColumnsByType<T>(this IQueryable<T> query) where T : new() {
Type type = typeof(T);
List<string> selectedProps = type.GetProperties().Select(p => p.Name).ToList();
Tuple<IQueryable, Type> anonObjectTypePair = query.SelectDynamicAndType(selectedProps);
IQueryable anonObjects = anonObjectTypePair.Item1;
Type anonType = anonObjectTypePair.Item2;
return anonObjects.Cast<object>().AsEnumerable().Select(ob => {
var ret = new T();
selectedProps.ForEach(p =>
type.GetProperty(p).SetValue(ret, anonType.GetField(p).GetValue(ob)));
return ret;
});
}
/// <summary>
/// Constructs a query that selects only the <paramref name="propNames"/> given and returns an <see cref="IQueryable"/> of dynamic objects with only the selected fields.
///
/// Also returns the type information of the dynamic objects.
/// </summary>
/// <param name="source">Source query.</param>
/// <param name="propNames">The list of properties names to select.</param>
/// <returns>A query of anonymous types defined by the supplied <paramref name="propNames"/> and the actual <see cref="Type"/> used to construct anonymous type.</returns>
public static Tuple<IQueryable, Type> SelectDynamicAndType(this IQueryable source, IEnumerable<string> propNames) {
Dictionary<string, PropertyInfo> sourceProperties = propNames.ToDictionary(name => name, name => source.ElementType.GetProperty(name));
Type dynamicType = LinqRuntimeTypeBuilder.GetDynamicType(sourceProperties.Values);
ParameterExpression sourceItem = Expression.Parameter(source.ElementType, "t");
IEnumerable<MemberBinding> bindings = dynamicType.GetFields().Select(p => Expression.Bind(p, Expression.Property(sourceItem, sourceProperties[p.Name]))).OfType<MemberBinding>();
Expression selector = Expression.Lambda(Expression.MemberInit(
Expression.New(dynamicType.GetConstructor(Type.EmptyTypes)), bindings), sourceItem);
return Tuple.Create(source.Provider.CreateQuery(Expression.Call(typeof(Queryable), "Select", new Type[] { source.ElementType, dynamicType },
Expression.Constant(source), selector)), dynamicType);
}
/// <summary>
/// Constructs a query that selects only the <paramref name="propNames"/> given and returns an <see cref="IQueryable{dynamic}"/> of dynamic objects with only the selected fields.
/// </summary>
/// <param name="source">Source query.</param>
/// <param name="propNames">The list of properties names to select.</param>
/// <returns>A query of anonymous types defined by the supplied <paramref name="propNames"/>.</returns>
public static IQueryable<dynamic> SelectDynamic(this IQueryable source, IEnumerable<string> propNames) {
return source.SelectDynamicAndType(propNames).Item1.Cast<dynamic>();
}
static class LinqRuntimeTypeBuilder {
private static AssemblyName assemblyName = new AssemblyName() { Name = "DynamicLinqTypes" };
private static ModuleBuilder moduleBuilder = null;
private static Dictionary<string, Type> builtTypes = new Dictionary<string, Type>();
static LinqRuntimeTypeBuilder() {
moduleBuilder = Thread.GetDomain().DefineDynamicAssembly(assemblyName, AssemblyBuilderAccess.Run).DefineDynamicModule(assemblyName.Name);
}
private static string GetTypeKey(Dictionary<string, Type> fields) {
string key = string.Empty;
foreach (var field in fields.OrderBy(kvp => kvp.Key).ThenBy(kvp => kvp.Value.Name))
key += field.Key + ";" + field.Value.Name + ";";
return key;
}
private static Type GetDynamicType(Dictionary<string, Type> fields) {
if (null == fields)
throw new ArgumentNullException("fields");
if (0 == fields.Count)
throw new ArgumentOutOfRangeException("fields", "fields must have at least 1 field definition");
try {
Monitor.Enter(builtTypes);
string className = GetTypeKey(fields);
if (builtTypes.ContainsKey(className))
return builtTypes[className];
TypeBuilder typeBuilder = moduleBuilder.DefineType(className, TypeAttributes.Public | TypeAttributes.Class | TypeAttributes.Serializable);
foreach (var field in fields)
typeBuilder.DefineField(field.Key, field.Value, FieldAttributes.Public);
builtTypes[className] = typeBuilder.CreateType();
return builtTypes[className];
} catch (Exception ex) {
//log.Error(ex);
Console.WriteLine(ex);
} finally {
Monitor.Exit(builtTypes);
}
return null;
}
public static Type GetDynamicType(IEnumerable<PropertyInfo> fields) {
return GetDynamicType(fields.ToDictionary(f => f.Name, f => f.PropertyType));
}
}
}
이것은 불행하게도, 당신보다 더 열심히이 수도 적어도 LINQ to Entities에서 기대할 수 있습니다. Entity SQL에서는 OFTYPE (ONLY ...)을 사용할 수 있습니다. Alex James는이 작업을 수행하는 방법을 설명합니다 (http://blogs.msdn.com/alexj/archive/2009/09/17/tip-35-how-to-write-oftypeonly-tentity.aspx "팁 35 - OfTypeOnly 작성 방법 <TEntity>() "). –