I am trying to dynamically build a predicate to only hydrate a subset of lists. But I am getting and error.
var predicate = PredicateBuilder.False<SP.List>();
var listTitles = new[] { "List One", "List Two" };
foreach (var listTitle in listTitles)
{
predicate = predicate.Or(x => x.Title == listTitle);
}
var lists = ctx.LoadQuery(ctx.Web.Lists.Where(predicate));
ctx.ExecuteQuery();
Error: The expression x is not supported
What am I missing?
Related
I want to add a dummy member to an IQueryable and came up with this solution:
IQueryable<Geography> geographies = _unitOfWork.GeographyRepository.GetAll(); //DbSet<Geography>
var dummyGeographies = new Geography[] { new Geography { Id = -1, Name = "All" } }.AsQueryable();
var combinedGeographies = geographies.Union(dummyGeographies);
var test = combinedGeographies.ToList(); //throws runtime exc
But it throws the following exception:
Processing of the LINQ expression 'DbSet
.Union(EnumerableQuery { Geography, })' by 'NavigationExpandingExpressionVisitor' failed. This may indicate either a bug or a limitation in EF Core.
How could I make it work?!
you can only union on data structure which are the same
IQueryable is only applicable if the query expression not been been expressed (ToList) before its run against db and you want the expression modifiable . aka nothing which which is not going to db as a query needs to be IQueryable (simple explanation better to research and understand this yourself)
List<Geography> geographies = _unitOfWork.GeographyRepository
.GetAll() //DbSet<Geography>
.Select(o => new Geography { Id = o.Id, Name = o.Name })
.ToList();
List<Geography> dummyGeographies = new List<Geography>() {
new Geography[] { new Geography { Id = -1, Name = "All" } }
};
var combinedGeographies = geographies.Union(dummyGeographies);
var test = combinedGeographies.ToList();
I was able to achieve it with the following code:
IQueryable<Geography> geographies = _unitOfWork.GeographyRepository.GetAll().Select(o => new Geography { Id = o.Id, Name = o.Name });
IQueryable<Geography> dummyGeographies = _unitOfWork.GeographyRepository.GetAll().Select(o => new Geography { Id = -1, Name = "All" });
var combinedGeographies = geographies.Union(dummyGeographies);
***ctx.Load(listItemCollection,
eachItem => eachItem.Include(
item => item,
item => item["Column1"],
item => item["Column2"]
));***
i have list of fields in a array of string instead of column1 and column2, how can i pass it through in include linq, not able to create proper lambda on runtime. i tried following ways but couldn't get success. Static befor loops works but thw fields added in loop fails as it doesn't evaluate string value in loop
***Expression<Func<ListItem, object>>[] paramss = new
Expression<Func<ListItem, object>>[length];
paramss[0] = x => x.ContentType;
paramss[1] = x => x["Title"];
count = 2;
foreach (string item in solConnDefModel.Columns)
{ paramss[count] = x => x[item];
count++;
}***
Please take a reference of below code:
List dlist = context.Web.Lists.GetByTitle("listname");
context.Load(dlist);
context.ExecuteQuery();
string[] fieldNames = { "Id", "Title", "num", "mStartDate" };
// Create the expression used to define the fields to be included
List<Expression<Func<ListItemCollection, object>>> fieldsToBeIncluded = new List<Expression<Func<ListItemCollection, object>>>();
foreach (string s in fieldNames)
{
fieldsToBeIncluded.Add(items => items.Include(item => item[s]));
}
// Initialize the collection of list items
var listItems = dlist.GetItems(new CamlQuery());
context.Load(listItems, fieldsToBeIncluded.ToArray());
context.ExecuteQuery();
You can hover on load method to see what type parameter it requires, then generate a corresponding one and pass it.
i have to create lambda expression at runtime. following code i was able to get expected value
Expression<Func<ListItem, object>>[] paramss = new Expression<Func<ListItem, object>>[length];
foreach (string item in Columns)
{
if (item.ToLower() != "contenttype")
{
ParameterExpression parameter = Expression.Parameter(typeof(ListItem), "x");
var propertyInfo = typeof(ListItem).GetMethod("get_Item");
var arguments = new List<Expression> { Expression.Constant(item) };
var expression = Expression.Call(parameter, propertyInfo, arguments);
var lambda = Expression.Lambda<Func<ListItem, object>>(expression, parameter);
paramss[count] = lambda;
}
else
{
paramss[count] = x => x.ContentType;
}
count++;
}
I'm creating an expression tree builder to return custom anonymous types. I tried it first with discrete types and it works ok, but using TypeBuilder to build types at runtime and pass that type to the expression tree fail with this error
'Argument expression is not valid'
here is the code I use:
this method I use to create the anonymous type
private Type CreateAnonymousType(Dictionary<string, Type> properties)
{
AssemblyName dynamicAssemblyName = new AssemblyName("MyAssembly");
AssemblyBuilder dynamicAssembly = AssemblyBuilder.DefineDynamicAssembly(dynamicAssemblyName, AssemblyBuilderAccess.Run);
ModuleBuilder dynamicModule = dynamicAssembly.DefineDynamicModule("MyAssembly");
TypeBuilder dynamicAnonymousType = dynamicModule.DefineType("ReturnType", TypeAttributes.Public | TypeAttributes.Class | TypeAttributes.AutoClass);
foreach (var p in properties)
{
dynamicAnonymousType.DefineField(p.Key, p.Value, FieldAttributes.Public);
}
return dynamicAnonymousType.CreateType();
}
and here is how I create the expression tree
var cars = new List<Car>();
for (int i = 0; i < 10; i++)
{
cars.Add(new Car { Id = i, Name = "Car " + i, Age = 2010 + i });
}
IQueryable<Car> allCars = cars.AsQueryable();
var properties = new Dictionary<string, Type>
{
{ "Id", typeof(int) },
{ "Name", typeof(string) }
};
ParameterExpression x = Expression.Parameter(typeof(Car), "x");
var listMembers = properties.Select(p => Expression.Property(x, p.Key));
var returnType = CreateAnonymousType(properties);
object destObject = Activator.CreateInstance(returnType);
var listBind = listMembers.Select(p => Expression.Bind(returnType.GetField(p.Member.Name), p));
var result = Expression.New(returnType);
var initExp = Expression.MemberInit(result, listBind.ToArray());
var call = Expression.Call(typeof(Queryable), "Select",
new Type[] {
typeof(Car),
returnType
}
, Expression.Constant(allCars)
, Expression.Lambda(initExp, x));
var qResult = allCars.Provider.CreateQuery<IdName>(call);
foreach (var car in qResult)
{
Console.WriteLine(car.Id + " - " + car.Name);
}
the error happened while CreateQuery method executes
This is because call returns dynamically created ReturnType not IdName thus the exception. Additionally you cannot put such dynamic types like ReturnType as generic type parameters because compiler knows nothing about them so you should use dynamic instead so the type will be resolved at runtime:
var qResult = allCars.Provider.CreateQuery<dynamic>(call);
I have a problem with a query. I have a List with int and want to use it to get the values from my dictionary. The dictionary-keys are int and some of them have the value of the list-items. My question is how i get the objects out of the dictionary, thats keys matces the list items. Was programming JAVA the last years and now struggling with LINQ :(
Thanks in advance
Problem solved. Thank you all :)
No idea how to close this topic. I am reading stackoverflow since one year, but this was my first post.
You can use Linq to join list items with dictionary KeyValuePair entries on entry key. And then select entry value from each joined pair:
var values = from l in list
join kvp in dictionary on l equals kvp.Key
select kvp.Value;
Lambda syntax:
var values = list.Join(dictionary, l => l, kvp => kvp.Key, (l,kvp) => kvp.Value);
Basically:
var value = dictionary[integerKey];
Or:
if (dictionary.TryGetValue(integerKey, out value)) {
}
You can also create an extension method:
public static class DictionaryExtensions
{
public static IEnumerable<TValue> FilterValuesBy<TKey, TValue>(this IDictionary<TKey, TValue> dictionary, IEnumerable<TKey> filter)
{
if (dictionary == null) throw new ArgumentNullException("dictionary");
if (filter == null) throw new ArgumentNullException("filter");
var coll = filter as ICollection<TKey> ?? new HashSet<TKey>(filter);
return dictionary.Where(kvp => coll.Contains(kvp.Key)).Select(kvp => kvp.Value);
}
}
Usage:
class Program
{
static void Main()
{
var dict = Enumerable.Range(0, 10).ToDictionary(x => x);
var filter = Enumerable.Range(0, 2);
foreach (var i in dict.FilterValuesBy(filter))
{
Console.WriteLine(i);
}
Console.ReadLine();
}
}
Simple Linq method chain:
var dict = Enumerable.Range(0, 10).ToDictionary(x => x);
var filter = Enumerable.Range(0, 2).ToList();
var filtered = dict.Where(x => filter.Contains(x.Key)).Select(x => x.Value).ToList();
I need to filter the ObservableCollection using LINQ Where clause in my Silverlight application.
The object type is dynamically created using method provided in following url.
http://mironabramson.com/blog/post/2008/06/Create-you-own-new-Type-and-use-it-on-run-time-(C).aspx
Is filtering my collection using Where clause for specific property possible?
How can I achieve it?
Thanks
The only way I know is using reflection, like this:
// using a list of dynamic types
var items = new List<object> { new { A = 0, B = 1 }, new { A = 1, C = 0 } };
// select ao items with A > 0
var filteredItems = items.Where(obj => (int)obj.GetType().GetField("A").GetValue(obj) > 0).ToArray();
// if you have a property instead of field, you should call GetProperty(), like this:
obj.GetType().GetProperty("PropertyName").GetValue(obj, null)
As you know the element type of your collection only at run time it probably is object at compile time. So the argument to the .Where method has to be a Func<object, bool>.
Here's a piece of code that will create such a delegate given a property of the actual element type and a lambda expression on the property (which i suppose you know the type of):
/// <summary>
/// Get a predicate for a property on a parent element.
/// </summary>
/// <param name="property">The property of the parent element to get the value for.</param>
/// <param name="propertyPredicate">The predicate on the property value.</param>
static Func<object, bool> GetPredicate<TProperty>(PropertyInfo property, Expression<Func<TProperty, bool>> propertyPredicate)
{
if (property.PropertyType != typeof(TProperty)) throw new ArgumentException("Bad property type.");
var pObj = Expression.Parameter(typeof(object), "obj");
// ((elementType)obj).property;
var xGetPropertyValue = Expression.Property(Expression.Convert(pObj, property.DeclaringType), property);
var pProperty = propertyPredicate.Parameters[0];
// obj => { var pProperty = xGetPropertyValue; return propertyPredicate.Body; };
var lambda = Expression.Lambda<Func<object, bool>>(Expression.Block(new[] { pProperty }, Expression.Assign(pProperty, xGetPropertyValue), propertyPredicate.Body), pObj);
return lambda.Compile();
}
Sample usage:
var items = new List<object> { new { A = 0, B = "Foo" }, new { A = 1, B = "Bar" }, new { A = 2, B = "FooBar" } };
var elementType = items[0].GetType();
Console.WriteLine("Items where A >= 1:");
foreach (var item in items.Where(GetPredicate<int>(elementType.GetProperty("A"), a => a >= 1)))
Console.WriteLine(item);
Console.WriteLine();
Console.WriteLine("Items where B starts with \"Foo\":");
foreach (var item in items.Where(GetPredicate<string>(elementType.GetProperty("B"), b => b.StartsWith("Foo"))))
Console.WriteLine(item);
Output:
Items where A >= 1:
{ A = 1, B = Bar }
{ A = 2, B = FooBar }
Items where B starts with "Foo":
{ A = 0, B = Foo }
{ A = 2, B = FooBar }