c# - Entity Framework is sometimes not loading the contents of Child Objects/Collections -

i've started have problem child collections in entity framework not being loaded lazy loading.

the prominent example of orders object - each order has 1 or more order lines associated (ie. list of products have been ordered , how many). sometimes, when program run, can open orders , order lines (for every order) blank. restart program, , might re-appear. it's pretty intermittent.

i have confirmed there no entries in child collection through logging & debugging:

    private observablecollection<orderline> loadorderlines()     {         log.debug("loading {0} order lines...", this.model.orderlines.count);          var result = new observablecollection<orderline>();          foreach (var orderline in this.model.orderlines)         {             result.add(orderline);         }          return result;     } 

sometimes "loading 0 order lines..." , "loading 4 order lines..." same order.

i can't use eager loading when load list of orders because don't want load order lines orders when few of them might ever opened - need keep loading fast possible , load things needed, hence lazy loading.

it's not orders object happening on, happens on other child collections too, effect same.

anybody have idea why ef doing , can fix it? it's huge problem - can't have empty order lines in program when should there!

extra info may or not of use:

this wpf mvvm application. data layer, shared website, uses repository/unit of work pattern.

in ordersrepository:

    public ienumerable<order> getorders(datetime fromdate, datetime todate, ienumerable<string> sources, bool? paidstatus, bool? shippedstatus, bool? cancelledstatus, bool? pendingstatus)     {         if (sources == null)         {             sources = this.context.ordersources.select(s => s.sourceid);         }          return             this.context.orders.where(                 o =>                 o.orderdate >= fromdate                 && o.orderdate < todate                 && sources.contains(o.sourceid)                 && (!paidstatus.hasvalue || ((o.receiptid != null) == paidstatus.value))                 && (!shippedstatus.hasvalue || ((o.shippeddate != null) == shippedstatus.value))                 && (!pendingstatus.hasvalue || (o.ispending == pendingstatus.value))                 && (!cancelledstatus.hasvalue || (o.cancelled == cancelledstatus.value))).orderbydescending(                     o => o.orderdate);     } 

the ordersviewmodel loads orders, creates orderviewmodel each 1 , puts them in observablecollection:

var orderslist = this.unitofwork.ordersrepository.getorders(this.filter).tolist();          foreach (var order in orderslist)         {             var viewmodel = this.viewmodelprovider.getviewmodel<orderviewmodel, order>(order);              this.orders.add(viewmodel);         } 

lazy loading loading related entities automatically when acces navigation property. but, in case, you're not doing automatically, manually.

to so, can disable lazy loading, , use explicit loading, this:

context.entry(order).collection(o => o.orderlines).load(); 

(besides, using technique, can apply filters).

your problem lazy loading can consequence of long lived dbcontext caches related entities @ given point in time, , reuses cache later, without hitting db, it's outdated. i.e. 1 dbcontext finds 3 order lines order , caches them. else, (outside db context), adds 2 new order lines order. access order lines first db context , outdated 3 order lines, instead of 5 there in db. there several ways in wich could, thoretically, reload/refresh cached data on dbcontext, can trouble. you'd rather use explicit loading suggested above. if see docs load method, can read this:

loads collection of entities database. note entities exist in context not overwritten values database.

however, safest option dispose dbcontext , create new one. (read second sentence of block above).