I am new in Elasticsearch.
I need to insert documents using bulk option using NEST api.
I have to index 5000 documents from a table. Below is the code that i use for bulk indexing.
public ActionResult CreateBulk()
{
var descriptor = new BulkDescriptor();
foreach (var test in db.Attendance.Take(5000).ToList())
{
descriptor.Index<Attendance>(op => op.Document(new Attendance
{
AttendanceId = test.AttendanceId,
AttendanceDate = test.AttendanceDate,
Estate = test.Estate,
Division = test.Division,
FieldNo = test.FieldNo,
Employee = test.Employee,
Activity = test.Activity,
Quantity = test.Quantity
}));
}
var bulkresult = ElasticClient.Bulk(descriptor);
return RedirectToAction("Index");
}
But when i run the code, i am getting the following error:
System.NullReferenceException was unhandled by user code
HResult=-2147467261
Message=Object reference not set to an instance of an object.
Source=Nest
StackTrace:
at Nest.NestSerializer.SerializeBulkDescriptor(IBulkRequest bulkRequest) in c:\Users\gmarz\code\elasticsearch-net\src\Nest\ExposedInternals\NestSerializer.cs:line 166
at Nest.ElasticClient.<Bulk>b__1b6(ElasticsearchPathInfo`1 p, BulkDescriptor d) in c:\Users\gmarz\code\elasticsearch-net\src\Nest\ElasticClient-Bulk.cs:line 31
at Nest.ElasticClient.Dispatch[D,Q,R](D descriptor, Func`3 dispatch) in c:\Users\gmarz\code\elasticsearch-net\src\Nest\ElasticClient.cs:line 82
at Nest.ElasticClient.Dispatch[D,Q,R](Func`2 selector, Func`3 dispatch) in c:\Users\gmarz\code\elasticsearch-net\src\Nest\ElasticClient.cs:line 70
at Nest.ElasticClient.Bulk(Func`2 bulkSelector) in c:\Users\gmarz\code\elasticsearch-net\src\Nest\ElasticClient-Bulk.cs:line 27
at AttendancePOC.Controllers.AttendanceController.CreateBulk() in D:\GIT Source\ElasticSearch\AttendancePOC\AttendancePOC\Controllers\AttendanceController.cs:line 114
at lambda_method(Closure , ControllerBase , Object[] )
at System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object[] parameters)
at System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary`2 parameters)
at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters)
at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass42.<BeginInvokeSynchronousActionMethod>b__41()
at System.Web.Mvc.Async.AsyncResultWrapper.<>c__DisplayClass8`1.<BeginSynchronous>b__7(IAsyncResult _)
at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult`1.End()
at System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethod(IAsyncResult asyncResult)
at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass37.<>c__DisplayClass39.<BeginInvokeActionMethodWithFilters>b__33()
at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass4f.<InvokeActionMethodFilterAsynchronously>b__49()
InnerException:
Please help me.. Is anything wrong in my code?.
I had the same exact problem.
I forgot about setting up the index name for this query.
I had set up a configuration which was setting up a default index during creation of new ElasticClient, but the configuration changed and my index was null.
Hope that helps
Please add default index like this
connectionSettings = new ConnectionSettings(connectionPool).DefaultIndex("indexname")
I do something like this :
var node = new Uri(elasticSearchURI);
var connectionPool = new SniffingConnectionPool(new[] { node });
var config = new ConnectionSettings(connectionPool)
.SniffOnConnectionFault(false)
.SniffOnStartup(false)
.SetTimeout(600000)
.DisablePing();
var EsClient = new ElasticClient(config);
Then i create the index and after that i use something like this:
List<Categories> categList = new List<Categories>();
if (categoriesData != null)
{
Parallel.ForEach(categoriesData, element =>
{
Categories inf = new Categories();
inf.Code = element.Code;
inf.Level = element.Level;
lock(categList)
{
categList.Add(inf);
}
});
EsClient.IndexMany<Categories>(categList,"index_name","type_name")
}
I had this problem and the solution was to include the defaultIndex property in ConnectionSettings as stated here eg:
var node = new Uri("http://something:9200");
var settings = new ConnectionSettings(node, "someDefaultIndexValue");
var client = new ElasticClient(settings);
Related
I have a generic func that takes a string of fields and selects them from an object using linq. However the output is not type of object but a subset of. So to convert this new List<subsetOfOriginal> to a DataTable, I cannot use list.GetType() because it will get me Original.
I have converted
Func<T, T> CreateSelectStatement<T>(string fields)
to
Func<T, S> CreateSelectStatement<T, S>(string fields)
because I don't want TResult to be of type T. Not sure if this is the correct way. This is the code I have at the moment and how it is invoked.
Func<T, S> CreateSelectStatement<T, S>(string fields)
{
var xParameter = Expression.Parameter(typeof(T), "o");
var xNew = Expression.New(typeof(T));
var bindings = fields.Split(',').Select(o => o.Trim())
.Select(o => {
var mi = typeof(T).GetProperty(o);
var xOriginal = Expression.Property(xParameter, mi);
return Expression.Bind(mi, xOriginal);
}
);
var xInit = Expression.MemberInit(xNew, bindings);
var lambda = Expression.Lambda<Func<T, S>>(xInit, xParameter);
return lambda.Compile();
}
and then to invoke it I'm using
CreateSelectStatement<SP_ProjectAnalysis_NP, dynamic>(columns)
Expected outcome should be the fields that are loading correctly but the type of the object is as if I used p => new { }. Currently I am getting object as the return type and trying to perform the following gets me 0 properties:
private static DataTable ToDataTable<T>(IList<T> list, string tableName = "table")
{
PropertyDescriptorCollection props = TypeDescriptor.GetProperties(typeof(T));
i would like to reconstruction my last project.
in past, i did't use any Web API.
can i just use the ODataQueryOptions to do $filter, $orderby , $top ,$skip
for my query in my own handler.ashx ?
some thing like.
var option = new ODataQueryOptions(request.params);
var query = option.ApplyTo(db.products);
Based on sfuqua's answer above I made my own helper class that builds OdataQueryOptions class based on Odata Uri:
using System.Linq;
using System.Net.Http;
using System.Web.Http.OData;
using System.Web.Http.OData.Builder;
using System.Web.Http.OData.Query;
namespace OdataHelpers
{
public static class ODataBuilder<T>
{
public static ODataQueryOptions<T> BuildOptions(string oDataUri)
{
var baseUri = "";
var odUri = "";
var spl = oDataUri.Split('?');
if (spl.Count() == 0)
odUri = spl[0];
else
{
baseUri = spl[0];
odUri = spl[1];
}
if (string.IsNullOrEmpty(baseUri))
baseUri = "http://localhost/api/" + typeof(T).Name;
var request = new HttpRequestMessage(HttpMethod.Get, baseUri + "?" + oDataUri.Replace("?", ""));
var modelBuilder = new ODataConventionModelBuilder();
modelBuilder.AddEntity(typeof(T));
var edmModel = modelBuilder.GetEdmModel();
var oDataQueryContext = new ODataQueryContext(edmModel, typeof(T));
return new ODataQueryOptions<T>(oDataQueryContext, request);
}
}
}
Example use:
var OdataStuff = ODataBuilder<CustomerIntView>.BuildOptions("$orderby=Id");
One way to accomplish this is by manually constructing the request URI and setting that in the request parameter of the ODataQueryOptions constructor. So this may not be precisely what the original poster was looking for (question needed some clarification).
In my case I have a unit test, and I wanted to validate that the odata options were being applied to my queryable object. In the following sample code, assume that you are testing a ProductController that has a ProductName field in it.
// Manually set an OData query parameter
const string restUrl = "http://localhost/api/product?$orderby=ProductName";
// Need to construct an HTTP Context and a Request, then inject them into the controller
var config = new HttpConfiguration();
var request = new HttpRequestMessage(HttpMethod.Post, restUrl);
var route = config.Routes.MapHttpRoute(WebApiConfig.DefaultRouteName, "api/{controller}/{id}");
var routeData = new HttpRouteData(route, new HttpRouteValueDictionary { { "controller", "Product" } });
var controller = new ProductController()
{
Request = request,
ControllerContext = new HttpControllerContext(config, routeData, request),
Url = new UrlHelper(request)
};
// Build up the OData query parameters
var modelBuilder = new ODataConventionModelBuilder();
modelBuilder.AddEntity(typeof(Product));
var edmModel = modelBuilder.GetEdmModel();
var oDataQueryContext = new ODataQueryContext(edmModel, typeof(Product));
var oDataQueryOptions = new ODataQueryOptions<Product>(oDataQueryContext, _controller.Request);
// Finally, call the controller
var result = controller.Get(oDataQueryOptions);
I do think you can if you can constructor an instance of ODataQueryOptions.
But, What's this:
var option = new ODataQueryOptions(request.params);
Web API doesn't provide such constructor. Is it your own implementation?
Thanks.
I followed this example Changing schema name on runtime - Entity Framework where I can create a new EntityConnection from a MetaDataWorkspace that I then use to construct a DbContext with a different schema, but I get compiler warnings saying that RegisterItemCollection method is obsolete and to "Construct MetadataWorkspace using constructor that accepts metadata loading delegates."
How do I do that? Here is the code that is working but gives the 3 warnings for the RegsiterItemCollection calls. I'm surprised it works since warning says obsolete not just deprecated.
public static EntityConnection CreateEntityConnection(string schema, string connString, string model)
{
XmlReader[] conceptualReader = new XmlReader[]
{
XmlReader.Create(
Assembly
.GetExecutingAssembly()
.GetManifestResourceStream(model + ".csdl")
)
};
XmlReader[] mappingReader = new XmlReader[]
{
XmlReader.Create(
Assembly
.GetExecutingAssembly()
.GetManifestResourceStream(model + ".msl")
)
};
var storageReader = XmlReader.Create(
Assembly
.GetExecutingAssembly()
.GetManifestResourceStream(model + ".ssdl")
);
//XNamespace storageNS = "http://schemas.microsoft.com/ado/2009/02/edm/ssdl"; // this would not work!!!
XNamespace storageNS = "http://schemas.microsoft.com/ado/2009/11/edm/ssdl";
var storageXml = XElement.Load(storageReader);
foreach (var entitySet in storageXml.Descendants(storageNS + "EntitySet"))
{
var schemaAttribute = entitySet.Attributes("Schema").FirstOrDefault();
if (schemaAttribute != null)
{
schemaAttribute.SetValue(schema);
}
}
storageXml.CreateReader();
StoreItemCollection storageCollection =
new StoreItemCollection(
new XmlReader[] { storageXml.CreateReader() }
);
EdmItemCollection conceptualCollection = new EdmItemCollection(conceptualReader);
StorageMappingItemCollection mappingCollection =
new StorageMappingItemCollection(
conceptualCollection, storageCollection, mappingReader
);
//var workspace2 = new MetadataWorkspace(conceptualCollection, storageCollection, mappingCollection);
var workspace = new MetadataWorkspace();
workspace.RegisterItemCollection(conceptualCollection);
workspace.RegisterItemCollection(storageCollection);
workspace.RegisterItemCollection(mappingCollection);
var connectionData = new EntityConnectionStringBuilder(connString);
var connection = DbProviderFactories
.GetFactory(connectionData.Provider)
.CreateConnection();
connection.ConnectionString = connectionData.ProviderConnectionString;
return new EntityConnection(workspace, connection);
}
I was able to get rid of the 3 warning messages. Basically it wants you to register the collections in the constructor of the MetadataWorkspace.
There are 3 different overloads for MetadataWorkspace, I chose to use the one which requires to to supply a path (array of strings) to the workspace metadata. To do this I saved readers to temp files and reloaded them.
This is working for me without any warnings.
public static EntityConnection CreateEntityConnection(string schema, string connString, string model) {
var conceptualReader = XmlReader.Create(Assembly.GetExecutingAssembly().GetManifestResourceStream(model + ".csdl"));
var mappingReader = XmlReader.Create(Assembly.GetExecutingAssembly().GetManifestResourceStream(model + ".msl"));
var storageReader = XmlReader.Create(Assembly.GetExecutingAssembly().GetManifestResourceStream(model + ".ssdl"));
XNamespace storageNS = "http://schemas.microsoft.com/ado/2009/11/edm/ssdl";
var storageXml = XElement.Load(storageReader);
var conceptualXml = XElement.Load(conceptualReader);
var mappingXml = XElement.Load(mappingReader);
foreach (var entitySet in storageXml.Descendants(storageNS + "EntitySet")) {
var schemaAttribute = entitySet.Attributes("Schema").FirstOrDefault();
if (schemaAttribute != null) {
schemaAttribute.SetValue(schema);
}
}
storageXml.Save("temp.ssdl");
conceptualXml.Save("temp.csdl");
mappingXml.Save("temp.msl");
MetadataWorkspace workspace = new MetadataWorkspace(new List<String>(){
#"temp.csdl",
#"temp.ssdl",
#"temp.msl"
}
, new List<Assembly>());
var connectionData = new EntityConnectionStringBuilder(connString);
var connection = DbProviderFactories.GetFactory(connectionData.Provider).CreateConnection();
connection.ConnectionString = connectionData.ProviderConnectionString;
return new EntityConnection(workspace, connection);
}
Not wanting to create temp files which slows the process down, I found an alternate answer to this is fairly simple. I replaced these lines of code -
//var workspace2 = new MetadataWorkspace(conceptualCollection, storageCollection, mappingCollection);
var workspace = new MetadataWorkspace();
workspace.RegisterItemCollection(conceptualCollection);
workspace.RegisterItemCollection(storageCollection);
workspace.RegisterItemCollection(mappingCollection);
with this one line of code -
var workspace = new MetadataWorkspace(() => conceptualCollection, () => storageCollection, () => mappingCollection);
and that works fine.
I'm building a LINQ-based query generator.
One of the features is being able to specify an arbitrary server-side projection as part of the query definition. For example:
class CustomerSearch : SearchDefinition<Customer>
{
protected override Expression<Func<Customer, object>> GetProjection()
{
return x => new
{
Name = x.Name,
Agent = x.Agent.Code
Sales = x.Orders.Sum(o => o.Amount)
};
}
}
Since the user must then be able to sort on the projection properties (as opposed to Customer properties), I recreate the expression as a Func<Customer,anonymous type> instead of Func<Customer, object>:
//This is a method on SearchDefinition
IQueryable Transform(IQueryable source)
{
var projection = GetProjection();
var properProjection = Expression.Lambda(projection.Body,
projection.Parameters.Single());
In order to return the projected query, I'd love to be able to do this (which, in fact, works in an almost identical proof of concept):
return Queryable.Select((IQueryable<TRoot>)source, (dynamic)properProjection);
TRoot is the type parameter in SearchDefinition. This results in the following exception:
Microsoft.CSharp.RuntimeBinder.RuntimeBinderException:
The best overloaded method match for
'System.Linq.Queryable.Select<Customer,object>(System.Linq.IQueryable<Customer>,
System.Linq.Expressions.Expression<System.Func<Customer,object>>)'
has some invalid arguments
at CallSite.Target(Closure , CallSite , Type , IQueryable`1 , Object )
at System.Dynamic.UpdateDelegates.UpdateAndExecute3[T0,T1,T2,TRet]
(CallSite site, T0 arg0, T1 arg1, T2 arg2)
at SearchDefinition`1.Transform(IQueryable source) in ...
If you look closely, it's inferring the generic parameters incorrectly: Customer,object instead of Customer,anonymous type, which is the actual type of the properProjection expression (double-checked)
My workaround is using reflection. But with generic arguments, it's a real mess:
var genericSelectMethod = typeof(Queryable).GetMethods().Single(
x => x.Name == "Select" &&
x.GetParameters()[1].ParameterType.GetGenericArguments()[0]
.GetGenericArguments().Length == 2);
var selectMethod = genericSelectMethod.MakeGenericMethod(source.ElementType,
projectionBody.Type);
return (IQueryable)selectMethod.Invoke(null, new object[]{ source, projection });
Does anyone know of a better way?
Update: the reason why dynamic fails is that anonymous types are defined as internal. That's why it worked using a proof-of-concept project, where everything was in the same assembly.
I'm cool with that. I'd still like to find a cleaner way to find the right Queryable.Select overload.
The fix is so simple it hurts:
[assembly: InternalsVisibleTo("My.Search.Lib.Assembly")]
Here's my test as requested. This on a Northwind database and this works fine for me.
static void Main(string[] args)
{
var dc = new NorthwindDataContext();
var source = dc.Categories;
Expression<Func<Category, object>> expr =
c => new
{
c.CategoryID,
c.CategoryName,
};
var oldParameter = expr.Parameters.Single();
var parameter = Expression.Parameter(oldParameter.Type, oldParameter.Name);
var body = expr.Body;
body = RebindParameter(body, oldParameter, parameter);
Console.WriteLine("Parameter Type: {0}", parameter.Type);
Console.WriteLine("Body Type: {0}", body.Type);
var newExpr = Expression.Lambda(body, parameter);
Console.WriteLine("Old Expression Type: {0}", expr.Type);
Console.WriteLine("New Expression Type: {0}", newExpr.Type);
var query = Queryable.Select(source, (dynamic)newExpr);
Console.WriteLine(query);
foreach (var item in query)
{
Console.WriteLine(item);
Console.WriteLine("\t{0}", item.CategoryID.GetType());
Console.WriteLine("\t{0}", item.CategoryName.GetType());
}
Console.Write("Press any key to continue . . . ");
Console.ReadKey(true);
Console.WriteLine();
}
static Expression RebindParameter(Expression expr, ParameterExpression oldParam, ParameterExpression newParam)
{
switch (expr.NodeType)
{
case ExpressionType.Parameter:
var parameterExpression = expr as ParameterExpression;
return (parameterExpression.Name == oldParam.Name)
? newParam
: parameterExpression;
case ExpressionType.MemberAccess:
var memberExpression = expr as MemberExpression;
return memberExpression.Update(
RebindParameter(memberExpression.Expression, oldParam, newParam));
case ExpressionType.AndAlso:
case ExpressionType.OrElse:
case ExpressionType.Equal:
case ExpressionType.NotEqual:
case ExpressionType.LessThan:
case ExpressionType.LessThanOrEqual:
case ExpressionType.GreaterThan:
case ExpressionType.GreaterThanOrEqual:
var binaryExpression = expr as BinaryExpression;
return binaryExpression.Update(
RebindParameter(binaryExpression.Left, oldParam, newParam),
binaryExpression.Conversion,
RebindParameter(binaryExpression.Right, oldParam, newParam));
case ExpressionType.New:
var newExpression = expr as NewExpression;
return newExpression.Update(
newExpression.Arguments
.Select(arg => RebindParameter(arg, oldParam, newParam)));
case ExpressionType.Call:
var methodCallExpression = expr as MethodCallExpression;
return methodCallExpression.Update(
RebindParameter(methodCallExpression.Object, oldParam, newParam),
methodCallExpression.Arguments
.Select(arg => RebindParameter(arg, oldParam, newParam)));
default:
return expr;
}
}
Also, dynamic method resolution doesn't really do much for you in this case as there are only two very distinct overloads of Select(). Ultimately you just need to remember that you won't have any static type checking on your results since you don't have any static type information. With that said, this will also work for you (using the above code example):
var query = Queryable.Select(source, expr).Cast<dynamic>();
Console.WriteLine(query);
foreach (var item in query)
{
Console.WriteLine(item);
Console.WriteLine("\t{0}", item.CategoryID.GetType());
Console.WriteLine("\t{0}", item.CategoryName.GetType());
}
Ok, I'll admit that I don't entirely "get" lambda expressions and LINQ expression trees yet; a lot of what I'm doing is cutting and pasting and seeing what works. I've looked over lots of documentation, but I still haven't found the my "aha" moment yet.
With that being said...
I'm attempting to dynamically add a GroupBy expression to my Linq expression. I followed the question here:
Need help creating Linq.Expression to Enumerable.GroupBy
and tried to implement what I saw there.
First off, I've got entity classes for my database, and a table calledObjCurLocViewNormalized
I've got an method that does the initial call,
public IQueryable<ObjCurLocViewNormalized> getLocations()
{
IQueryable<ObjCurLocViewNormalized> res = (from loc in tms.ObjCurLocViewNormalized
select loc);
return res;
}
so I can call:
IQueryable<MetAmericanLinqDataModel.ObjCurLocViewNormalized> locations = american.getLocations();
No problem so far.
Now, I want to group by an arbitrary column, with a call like this:
var grouped = locations.addGroupBy(childLocationFieldName);
Right now, I have a method :
static public System.Linq.IQueryable<System.Linq.IGrouping<string, TResult>> addGroupBy<TResult>(this IQueryable<TResult> query, string columnName)
{
var providerType = query.Provider.GetType();
// Find the specific type parameter (the T in IQueryable<T>)
var iqueryableT = providerType.FindInterfaces((ty, obj) => ty.IsGenericType && ty.GetGenericTypeDefinition() == typeof(IQueryable<>), null).FirstOrDefault();
var tableType = iqueryableT.GetGenericArguments()[0];
var tableName = tableType.Name;
var data = Expression.Parameter(iqueryableT, "query");
var arg = Expression.Parameter(tableType, tableName);
var nameProperty = Expression.PropertyOrField(arg, columnName);
var lambda = Expression.Lambda<Func<TResult, string>>(nameProperty, arg);
var expression = Expression.Call(typeof(Enumerable),
"GroupBy",
new Type[] { tableType, typeof(string) },
data,
lambda);
var predicate = Expression.Lambda<Func<TResult, String>>(expression, arg); // this is the line that produces the error I describe below
var result = query.GroupBy(predicate).AsQueryable();
return result;
}
All this compiles ok, but when I run it, I get the error:
System.ArgumentException: Expression of type 'System.Collections.Generic.IEnumerable`1[System.Linq.IGrouping`2[System.String,MetAmericanLinqDataModel.ObjCurLocViewNormalized]]' cannot be used for return type 'System.String'
and the error comes from this line:
var predicate = Expression.Lambda<Func<TResult, String>>(expression, arg);
I'm copying and adapting this code from successful work I did in dynamically added Where clauses to an expression. So I'm sort of stabbing in the dark here.
If anyone out there can help to shed some light on this, Obviously posting complete working code and doing all my thinking for me would be great :), but if you could just lay out just why this is wrong, or how to wrap my head around these concepts, that would be great. If you can point to documentation that can really help be bridge the gap between the basics of lambda expressions, and building dynamic expression trees, that would be great. There's obviously big holes in my knowledge, but I think this information could be useful to others.
thanks everyone for your time, and of course if I find the answer elsewhere, I'll post it here.
Thanks again.
Don
The solution should be pretty simple:
public static IQueryable<IGrouping<TColumn, T>> DynamicGroupBy<T, TColumn>(
IQueryable<T> source, string column)
{
PropertyInfo columnProperty = typeof(T).GetProperty(column);
var sourceParm = Expression.Parameter(typeof(T), "x");
var propertyReference = Expression.Property(sourceParm, columnProperty);
var groupBySelector = Expression.Lambda<Func<T, TColumn>>(propertyReference, sourceParm);
return source.GroupBy(groupBySelector);
}
Assuming a sample class like this:
public class TestClass
{
public string TestProperty { get; set; }
}
You invoke it like this:
var list = new List<TestClass>();
var queryable = list.AsQueryable();
DynamicGroupBy<TestClass, string>(queryable, "TestProperty");
All that you need to do to make it work is the following:
static public IQueryable<IGrouping<TValue, TResult>> addGroupBy<TValue, TResult>(
this IQueryable<TResult> query, string columnName)
{
var providerType = query.Provider.GetType();
// Find the specific type parameter (the T in IQueryable<T>)
const object EmptyfilterCriteria = null;
var iqueryableT = providerType
.FindInterfaces((ty, obj) => ty.IsGenericType && ty.GetGenericTypeDefinition() == typeof(IQueryable<>), EmptyfilterCriteria)
.FirstOrDefault();
Type tableType = iqueryableT.GetGenericArguments()[0];
string tableName = tableType.Name;
ParameterExpression data = Expression.Parameter(iqueryableT, "query");
ParameterExpression arg = Expression.Parameter(tableType, tableName);
MemberExpression nameProperty = Expression.PropertyOrField(arg, columnName);
Expression<Func<TResult, TValue>> lambda = Expression.Lambda<Func<TResult, TValue>>(nameProperty, arg);
//here you already have delegate in the form of "TResult => TResult.columnName"
return query.GroupBy(lambda);
/*var expression = Expression.Call(typeof(Enumerable),
"GroupBy",
new Type[] { tableType, typeof(string) },
data,
lambda);
var predicate = Expression.Lambda<Func<TResult, String>>(expression, arg); // this is the line that produces the error I describe below
var result = query.GroupBy(predicate).AsQueryable();
return result;*/
}
And you will call you expression in the following manner:
var grouped = locations.addGroupBy<string, ObjCurLocViewNormalized>(childLocationFieldName);
First generic parameter "string" us used for saying explicilty what type of elements you a grouping on. For example you can group by "int" field and method call will be like following:
var grouped = locations.addGroupBy<int, ObjCurLocViewNormalized>(someFieldNameWithTheTypeOfInt);
Edit
Just to finish this solution your way:
//return query.GroupBy(lambda);
MethodCallExpression expression = Expression.Call(typeof (Enumerable),
"GroupBy",
new[] { typeof(TResult), typeof(TValue) },
data,
lambda);
var result = Expression.Lambda(expression, data).Compile().DynamicInvoke(query);
return ((IEnumerable<IGrouping<TValue, TResult>>)result).AsQueryable();