c# - Writing a basic Expression Builder -

i using linq-to-entities , 1 query requires property loaded dynamically. query looks this:

var found = context.integrateviews.groupby(x => x.typeofbed)                    .select(type => new typecounts                             { name = type.key, count = type.count() }).tolist(); 

the property on group clause being run typeofbed. want run query on different properties e.g., next time want run on, let's x.typeofchair , on. this, need have property in there dynamically.

i trying write expression builder this.

public expression<func<lookupfilteritem>> propertylambda(string propertyname) {     var param = expression.parameter(typeof(lookupfilteritem), "lookupitem");     //type of x in above example lookupfilteritem     var propertyexpression = expression.property(param, propertyname);      var returnexpr = expression.lambda<func<lookupfilteritem>>(propertyexpression);     return returnexpr;     //if pass string "typeofbed" method, expecting return     // lookupitem => lookupitem.typeofbed } 

and intend use this:

var found = context.integrateviews.groupby(propertylambda("typeofbed"))                    .select(type => new typecounts                             { name = type.key, count = type.count() }).tolist(); 

but not working, getting compile time error says:

error cs0411: type arguments method 'system.linq.queryable.groupby(system.linq.iqueryable, system.linq.expressions.expression>)' cannot inferred usage. try specifying type arguments explicitly.

what doing wrong here?

this seems syntax issue. try this:

public expression<func<lookupfilteritem, string>> propertylambda(string propertyname)     {         var param = expression.parameter(typeof(lookupfilteritem), "lookupitem");         var propertyexpression = expression.property(param, propertyname);         var returnexpr = expression.lambda<func<lookupfilteritem, string>>(propertyexpression, param);         return returnexpr;     } 

and usage:

var found = context.integrateviews.groupby(propertylambda("typeofbed").compile())                .select(type => new typecounts                         { name = type.key, count = type.count() }).tolist();