I'm currently messing about with generics and I'm trying to write a function that I can call to load everything from a database table simply by specifying the table name.
I'm most of the way there; my generic methods all seem to work, but I'm not quite sure how to cast my results into something usable.
This is the guts of the method so far:
private static List<EntityCodeBase> GetCodeLoadResults(CodeTables table)
{
List<EntityCodeBase> results = new List<EntityCodeBase>();
Assembly assm = Assembly.Load(new System.Reflection.AssemblyName("RR"));
Type tableType = assm.GetTypes().Where(u => u.Name.ToLower() == table.ToString().ToLower()).FirstOrDefault();
MethodInfo mi = typeof(SpecificEntity).GetMethod("LoadAll");
mi = mi.MakeGenericMethod(tableType);
mi.Invoke(null, null); //how can I cast the resulting object into a List<EntityCodeBase> ?
return results;
}
Assuming SpecificEntity.LoadAll returns a list of some type derived from EntityCodeBase, you can't cast directly to a List<EntityCodeBase> but you can cast to IEnumerable<EntityCodeBase>. Then you can create a new list:
var ecbList = (IEnumerable<EntityCodeBase>)mi.Invoke(null, null);
return list.ToList();
It might be cleaner however, if you can get the table name from the entity type, either directly by name, using attributes, or using a map. Then you can make GetCodeLoadResults generic in the result type e.g.
private static List<T> GetCodeLoadResults() where T : EntityCodeBase
{
Assembly assm = Assembly.Load(new System.Reflection.AssemblyName("RR"));
Type tableType = //get table type from T
MethodInfo mi = typeof(SpecificEntity).GetMethod("LoadAll");
mi = mi.MakeGenericMethod(tableType);
return (List<T>)mi.Invoke(null, null);
}
If you're not using .Net 4, you can't cast a List<TDerived> to an IEnumerable<TBase>, so you'll have to cast to IEnumerable first:
return ((System.Collections.IEnumerable)mi.Invoke(null, null))
.Cast<EntityCodeBase>()
.ToList();
Related
I have some methods that execute arbitrary SQL against a database and serialize that data collection into a list of a concrete type. That data is then serialized into JSON and stored in a cell in a table. Later, I need to come back and deserialize that data back into its original collection so that it can be used.
I'm having some issues figuring out how to take a Type object and create a collection of that type in order to deserialize it. Here is how my code operates:
public async Task ExecuteWidget(Guid runGuid, string widgetName, Type type, string sql,
IEnumerable<SqlParameter> parameters)
{
var report = operationsContext.ReportRuns.FirstOrDefault(n => n.RunGuid == runGuid);
CheckReportStatus(report);
var param = parameters.ToList();
var result = edwContext.Database.SqlQuery(type, sql, param.ToArray<object>());
var query = result.GetQuery(param);
var data = await result.ToListAsync();
var widgetData = new ReportRunWidgetData()
{
ReportRunId = report?.ReportRunId ?? -1, // This should never be null.
WidgetName = widgetName,
WidgetData = new JavaScriptSerializer().Serialize(data),
Query = query
};
operationsContext.ReportRunWidgetDatas.Add(widgetData);
await operationsContext.SaveChangesAsync();
}
My fetching logic looks something like this:
public object FetchWidgetData(Guid runGuid, string widgetName, Type dataType)
{
var data = operationsContext.ReportRuns
.Include("ReportRunWidgetDatas")
.FirstOrDefault(n => n.RunGuid == runGuid)?
.ReportRunWidgetDatas.FirstOrDefault(n => n.WidgetName == widgetName)?
.WidgetData;
if (data == null) return null;
var deserialized = new JavaScriptSerializer().Deserialize(data, dataType);
return deserialized;
}
Now when the ExecuteWidget method is called, the type parameter is populated by the widget's DTO datatype. For example HeadlineWidgetDTO. However, the execute command gets the data back as a List<HeadlineWidgetDTO>. When my FetchWidgetData method is called, the dataType supplied is still HeadlineWidgetDTO, but it actually needs to be of type IEnumerable<HeadlineWidgetDTO> to deserialize properly.
Given just the type for an individual data row, how can I create a Type object that is instead a collection of that type?
This is mostly a duplicate of How to use Activator to create an instance of a generic Type and casting it back to that type?, however it's hard to tell.
Basically, if you have a type object Type theType, you need to do something like:
var listType = typeof(List<>);
var typeParams = new [] {theType};
var listOfTType = listType.MakeGenericType(typeParams);
var newListOfT = Activator.CreateInstance(listOfTType);
At that point, you have a variable of type object, but that references an object of type List<WhateverYourTypeIs>. Say, theType is typeof(int), then you will have an object of List<int>. Casting it to something usuable is a whole other question though. If you want to add something to that list, I suspect the best way would be to get a MethodInfo for the Add method and Invoke it.
I thought of another way to do this if the type has a default constructor and isn't too expensive to create. Here's a sample (creating a List<int> - but that's just the way I have it coded):
var type = typeof(int);
var dummy = Activator.CreateInstance(type);
var listOfType = new[] {dummy}.ToList();
When you are finished, the listOfType variable is typed as a List<object> but refers to a List<int>. It's mostly mostly workable - for example, you can call Add(object someObj) on it. You won't get compile type parameter type checking, but you will be able to use it.
I have a stored procedure call interface that I'm using to handle results from stored procedures with entity (using Translate method to translate the results of our stored procedure into entities that can be tracked and used in EF as normal)
Here's the basic code...
List<object> current = new List<object>();
object item = ((Type)currenttype.Current).GetConstructor(System.Type.EmptyTypes).Invoke(new object[0]);
ObjectContext actualContext = ((IObjectContextAdapter)context).ObjectContext;
string className = "";
EntityContainer container = null;
string setName = "";
className = ((Type)currenttype.Current).ToString();
container = actualContext.MetadataWorkspace.GetEntityContainer(((IObjectContextAdapter)context).ObjectContext.DefaultContainerName, DataSpace.CSpace);
setName = (from meta in container.BaseEntitySets
where meta.ElementType.FullName == className
select meta.Name).FirstOrDefault();
var t = typeof(ObjectContext).GetMethod("Translate", new Type[] { typeof(DbDataReader), typeof(string), typeof(MergeOption) }).MakeGenericMethod(item.GetType()).Invoke(actualContext, new object[] { reader, setName, MergeOption.AppendOnly });
The issue is that I can't do anything with 't' that I want, it's type is listed as
object {System.Data.Entity.Core.Objects.ObjectResult<POCOClass>}. I can't call any of the normal methods that I can normally on the ObjectResult type such as ToArray or ToList.
I need a way to convert it into System.Data.Entity.Core.Objects.ObjectResult<POCOClass>. The difference being that 't' is listed as type object first.
I cannot use any strongly typed casts because the types will change depending on the stored procedure. I've tried using the dynamic keyword instead of var for t and I've also tried using Convert.ChangeType. It never changes from the object base type. dynamic t returns this the following error:
'System.Data.Entity.Core.Objects.ObjectResult<POCOClass>' does not contain a definition for 'ToList'
Thought I know for a fact it does...
To clear up confusion, here's a watch screenshot. The first line is what's being returned, I want it to be like the second (see Type column).
Edit: might be getting closer... I added this:
var listedT = typeof(Enumerable).GetMethod("ToList").MakeGenericMethod(item.GetType()).Invoke(null, new object[] { t });
current.AddRange(listedT); // Error here...
listedT becomes a object {System.Collections.Generic.List<ReportCatalog.Models.Catalog_Reports>} and I get the error, cannot convert from object to System.Collections.Generic.IEnumerable<object>.
Since ObjectResult<T> implements also the non-generic IEnumerable interface, cast it to this type and enumerate it.
var e = (IEnumerable)t;
foreach (object o in e) {
//TODO: use o
}
I get the name of the entity that I want to query at runtime so I use reflection to call SqlQuery<T>:
Assembly assm = typeof(DataAccessLayer.MyContext).Assembly;
Type myType = assm.GetTypes().SingleOrDefault(type => type.Name.Equals("Clients"));
MethodInfo genericMethod = typeof(System.Data.Entity.Database).GetMethods()
.Where(method => method.Name == "SqlQuery" && method.IsGenericMethod ==
true).FirstOrDefault();
MethodInfo generic = genericMethod.MakeGenericMethod(myType);
so this work fine I set my params - object[] args = { SomeQuery, new object[] { } };
and then I Invoke it - generic.Invoke(db.Database, args);.
The problem is when I try to get the actual records. I try to assign the invocation to a variable like this :
var records = generic.Invoke(db.Database, args);
but records is type of object and in fact the value of records is the sql query that I've passed in records the invokation. The Visual Studio is giving me option to load the results but it seems that it can be done only manually.
Then I tried with with using dynamic like :
dynamic records = generic.Invoke(db.Database, args);
which produce the same result, first records holds the string representation of my sql query, when I load the result I get the records as dynamic proxies but that's all. It's a little bit better since I can use foreach on records when the type is dynamic but I can't get nothing from this dynamic proxy that I get from the foreach.
At last I tried this :
Assembly assm = typeof(DataAccessLayer.BankAttachmentsEntities).Assembly;
Type myType = assm.GetTypes().SingleOrDefault(type => type.Name.Equals("Clients"));
var listType = typeof(List<>).MakeGenericType(myType);
var list = Activator.CreateInstance(listType);
Hoping that this will give me an instantiated variable of type List<Clients> but it seems not to be the case. Still it's recognized as object and I can't use ToList or other method that will load the result automatically.
How can I get access to the records fetched like this?
This is best explained using code. I have a generic class that has a method that returns an integer. Here is a simple version for the purposes of explaining...
public class Gen<T>
{
public int DoSomething(T instance)
{
// Real code does something more interesting!
return 1;
}
}
At runtime I use reflection to discover the type of something and then want to create an instance of my Gen class for that specific type. That is easy enough and done like this...
Type fieldType = // This is the type I have discovered
Type genericType = typeof(Gen<>).MakeGenericType(fieldType);
object genericInstance = Activator.CreateInstance(genericType);
I now want to create an Expression that will take as a parameter an instance of the generic type and then calls the DoSomething method of that type. So I want the Expression to effectively perform this...
int answer = genericInstance.DoSomething(instance);
...except I do not have the 'instance' until some point later at runtime and the genericInstance is the generated type as can be seen above. My attempt at creating the Lambda for this is as follows...
MethodInfo mi = genericType.GetMethod("DoSomething",
BindingFlags.Instance | BindingFlags.Public);
var p1 = Expression.Parameter(genericType, "generic");
var p2 = Expression.Parameter(fieldType, "instance");
var x = Expression.Lambda<Func<genericType, fieldType, int>>
(Expression.Call(p1, mi, p2),
new[] { p1, p2 }).Compile();
...so that later on I can call it with something like this...
int answer = x(genericInstance, instance);
Of course, you cannot provide Func with instance parameters and so I have no idea how to parameterize the Lambda generation. Any ideas?
I think you would just use the Expression.Lambda that takes the delegate type as a type rather then as a generic, and create your Func on the fly like you are with Gen<>:
MethodInfo mi = genericType.GetMethod("DoSomething",
BindingFlags.Instance | BindingFlags.Public);
var p1 = Expression.Parameter(genericType, "generic");
var p2 = Expression.Parameter(fieldType, "instance");
var func = typeof (Func<,,>);
var genericFunc = func.MakeGenericType(genericType, fieldType, typeof(int));
var x = Expression.Lambda(genericFunc, Expression.Call(p1, mi, p2),
new[] { p1, p2 }).Compile();
This will return a Delegate rather than a strongly typed Func, but you can of course cast it if needed (and seemingly difficult if you don't know what you are casting to), or dynamically invoke it using DynamicInvoke on it.
int answer = (int) x.DynamicInvoke(genericInstance, instance);
EDIT:
A good idea that does indeed work. Unfortunately the reason I want to use a strongly typed compiled Lambda is performance. Using DynamicInvoke is prettty slow compared to a typed Lambda.
This seems to work without the need of a dynamic invoke.
var p1 = Expression.Parameter(genericType, "generic");
var p2 = Expression.Parameter(fieldType, "instance");
var func = typeof(Func<,,>);
var genericFunc = func.MakeGenericType(genericType, fieldType, typeof(int));
var x = Expression.Lambda(genericFunc, Expression.Call(p1, mi, p2), new[] { p1, p2 });
var invoke = Expression.Invoke(x, Expression.Constant(genericInstance), Expression.Constant(instance));
var answer = Expression.Lambda<Func<int>>(invoke).Compile()();
EDIT 2:
A greatly simplified version:
Type fieldType = ;// This is the type I have discovered
Type genericType = typeof(Gen<>).MakeGenericType(fieldType);
object genericInstance = Activator.CreateInstance(genericType);
MethodInfo mi = genericType.GetMethod("DoSomething",
BindingFlags.Instance | BindingFlags.Public);
var value = Expression.Constant(instance, fieldType);
var lambda = Expression.Lambda<Func<int>>(Expression.Call(Expression.Constant(genericInstance), mi, value));
var answer = lambda.Compile()();
This answer only applies if you are using .NET 4.0.
If you make genericInstance dynamic instead of object, you can then call the DoSomething method on it directly, and the dynamic language runtime will take care of everything for you.
class Type1 {
public int DoSomething() { return 1; }
}
class Type2 {
public int DoSomething() { return 2; }
}
static void TestDynamic() {
dynamic t1 = Activator.CreateInstance(typeof(Type1));
int answer1 = t1.DoSomething(); // returns 1
dynamic t2 = Activator.CreateInstance(typeof(Type2));
int answer2 = t2.DoSomething(); // returns 2
}
If you need to keep this class structure (Gen<T>), then I don't see an easy way around the fact that you don't know the type T at compile time. If you want to call the delegate, you either have to know its full type at compile time, or you need to pass in the parameters as objects.
Using dynamic gets you to hide the complexity of getting the MethodInfo, etc., and gives you excellent performance. The one drawback vs. DynamicInvoke that I see is that I believe you get the initial overhead of resolving the dynamic call once for every call site. The bindings are cached so that they run very fast from the second time onwards if you call it on objects with the same type.
It's better to to accept an object and use convert to a known type.
Here is an example, how to build access to a property by name on unknown depth:
var model = new { A = new { B = 10L } };
string prop = "A.B";
var parameter = Expression.Parameter(typeof(object));
Func<object, long> expr = (Func<object, long>) Expression.Lambda(prop.Split('.').Aggregate<string, Expression>(Expression.Convert(parameter, model.GetType()), Expression.Property), parameter).Compile();
expr(model).Dump();
It avoids extra costs of DynamicInvoke when type of delegate is unknown at compile time.
I have a bunch of IEnumerable Collections which exact number and types is subject of frequent changes (due to automatic code generation).
It looks something like this:
public class MyCollections {
public System.Collections.Generic.IEnumerable<SomeType> SomeTypeCollection;
public System.Collections.Generic.IEnumerable<OtherType> OtherTypeCollection;
...
At runtime i want to determine each Type and it's count without having to rewrite the code after every code generation. So i am looking for a generic approach using reflection. The result i am looking for is something like:
MyType: 23
OtherType: 42
My problem is that i can't figure how to invoke the Count method properly. Here is what i have so far:
// Handle to the Count method of System.Linq.Enumerable
MethodInfo countMethodInfo = typeof(System.Linq.Enumerable).GetMethod("Count", new Type[] { typeof(IEnumerable<>) });
PropertyInfo[] properties = typeof(MyCollections).GetProperties();
foreach (PropertyInfo property in properties)
{
Type propertyType = property.PropertyType;
if (propertyType.IsGenericType)
{
Type genericType = propertyType.GetGenericTypeDefinition();
if (genericType == typeof(IEnumerable<>))
{
// access the collection property
object collection = property.GetValue(someInstanceOfMyCollections, null);
// access the type of the generic collection
Type genericArgument = propertyType.GetGenericArguments()[0];
// make a generic method call for System.Linq.Enumerable.Count<> for the type of this collection
MethodInfo localCountMethodInfo = countMethodInfo.MakeGenericMethod(genericArgument);
// invoke Count method (this fails)
object count = localCountMethodInfo.Invoke(collection, null);
System.Diagnostics.Debug.WriteLine("{0}: {1}", genericArgument.Name, count);
}
}
}
If you insist on doing it the hard way ;p
Changes:
how you obtain countMethodInfo for a generic method
the arguments to Invoke
Code (note obj is my instance of MyCollections):
MethodInfo countMethodInfo = typeof (System.Linq.Enumerable).GetMethods().Single(
method => method.Name == "Count" && method.IsStatic && method.GetParameters().Length == 1);
PropertyInfo[] properties = typeof(MyCollections).GetProperties();
foreach (PropertyInfo property in properties)
{
Type propertyType = property.PropertyType;
if (propertyType.IsGenericType)
{
Type genericType = propertyType.GetGenericTypeDefinition();
if (genericType == typeof(IEnumerable<>))
{
// access the collection property
object collection = property.GetValue(obj, null);
// access the type of the generic collection
Type genericArgument = propertyType.GetGenericArguments()[0];
// make a generic method call for System.Linq.Enumerable.Count<> for the type of this collection
MethodInfo localCountMethodInfo = countMethodInfo.MakeGenericMethod(genericArgument);
// invoke Count method (this fails)
object count = localCountMethodInfo.Invoke(null, new object[] {collection});
System.Diagnostics.Debug.WriteLine("{0}: {1}", genericArgument.Name, count);
}
}
}
That is going to involve some MakeGenericMethod - and a lot of reflection generally. Personally, I would be tempted to just simplify by ditching the generics in this case:
public static int Count(IEnumerable data) {
ICollection list = data as ICollection;
if(list != null) return list.Count;
int count = 0;
IEnumerator iter = data.GetEnumerator();
using(iter as IDisposable) {
while(iter.MoveNext()) count++;
}
return count;
}
You can cast to the non-generic IEnumerable trivially, even if fetching via reflection.
By now, the question has been answered, but I'd like to present you a trimmed down — and I think, rather trivial version — of the "calling a generic extension method", which can be used to invoke Count reflectively:
// get Enumerable (which holds the extension methods)
Type enumerableT = typeof(Enumerable);
// get the Count-method (there are only two, you can check the parameter-count as in above
// to be certain. Here we know it's the first, so I use the first:
MemberInfo member = enumerableT.GetMember("Count")[0];
// create the generic method (instead of int, replace with typeof(yourtype) in your code)
MethodInfo method = ((MethodInfo) member).MakeGenericMethod(typeof(int));
// invoke now becomes trivial
int count = (int)method.Invoke(null, new object[] { yourcollection });
The above works, because you don't need to use the generic type of IEnumerable<> to be able to invoke Count, which is an extension of Enumerable and takes an argument of IEnumerable<T> as first param (it's an extension), but you don't need to specify that.
Note that, from the reading of your question, it seems to me that you should actually use generics for your types, which adds type safety back into your project and still allows you to use Count or whatever. After all, the one thing that's certain is that all are Enumerable, right? If so, who needs reflection?
var count = System.Linq.Enumerable.Count(theCollection);
Edit: you say it's generated though, so can you not just generate a properties with calls to Count()?
public class MyCollections
{
public System.Collections.Generic.IEnumerable<SomeType> SomeTypeCollection;
public System.Collections.Generic.IEnumerable<OtherType> OtherTypeCollection;
public int CountSomeTypeCollection
{
get { return this.SomeTypeCollection.Count(); }
}
...