linq - Dynamically Adding a GroupBy to a Lambda Expression -

ok, i'll admit don't entirely "get" lambda expressions , linq expression trees yet; lot of i'm doing cutting , pasting , seeing works. i've looked on lots of documentation, still haven't found "aha" moment yet.

with being said...

i'm attempting dynamically add groupby expression linq expression. followed question here: need creating linq.expression enumerable.groupby

and tried implement saw there.

first off, i've got entity classes database, , table calledobjcurlocviewnormalized

i've got method initial call,

public iqueryable<objcurlocviewnormalized> getlocations() {     iqueryable<objcurlocviewnormalized> res = (from loc in tms.objcurlocviewnormalized                                select loc);     return res; } 

so can call:

iqueryable<metamericanlinqdatamodel.objcurlocviewnormalized> locations = american.getlocations(); 

no problem far.

now, want group arbitrary column, call this:

var grouped = locations.addgroupby(childlocationfieldname); 

right now, have 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 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); // line produces error describe below     var result = query.groupby(predicate).asqueryable();     return result; } 

all compiles ok, when run it, error:

system.argumentexception: expression of type 'system.collections.generic.ienumerable`1[system.linq.igrouping`2[system.string,metamericanlinqdatamodel.objcurlocviewnormalized]]' cannot used return type 'system.string' 

and error comes line:

 var predicate = expression.lambda<func<tresult, string>>(expression, arg); 

i'm copying , adapting code successful work did in dynamically added clauses expression. i'm sort of stabbing in dark here.

if out there can shed light on this, posting complete working code , doing thinking me great :), if lay out why wrong, or how wrap head around these concepts, great. if can point documentation can bridge gap between basics of lambda expressions, , building dynamic expression trees, great. there's big holes in knowledge, think information useful others.

thanks time, , of course if find answer elsewhere, i'll post here.

thanks again.

don

the solution should 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 sample class this:

public class testclass {     public string testproperty { get; set; } } 

you invoke this:

var list = new list<testclass>(); var queryable = list.asqueryable(); dynamicgroupby<testclass, string>(queryable, "testproperty");