How to combine 2different IQueryable/List/Collection with same base class? LINQ Union and Covariance issues -



How to combine 2different IQueryable/List/Collection with same base class? LINQ Union and Covariance issues -

i trying combine (union or concat) 2 lists/collection one. 2 lists have mutual base of operations class. e.g. i've tried this:

iqueryable<contractitem> contractitems = myrepository.retrievecontractitems(); iqueryable<changeorderitem> changeorderitems = myrepository.retrievechangeorderitems(); iqueryable<itembase> folderitems = contractitems.concat<itembase>(changeorderitems);

but getting linq error dbunionallexpression requires arguments compatible collection resulttypes.

anybody know how properly? thing google stackoverflow question: linq union objects same base of operations class

thanks.

use cast operator:

iqueryable<itembase> folderitems = contractitems.cast<itembase>().concat(changeorderitems.cast<itembase>());

the reply other question works linq objects, not linq entities or linq sql.

alternatively, can convert linq objects calling asenumerable:

iqueryable<itembase> folderitems = contractitems.asenumerable().concat<itembase>(changeorderitems);

however, take care in linq objects; concat work without overhead (iterating through both collections database), union pull 1 of collections exclusively database , iterate through other.

linq union covariance

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