c# - Assign an expression to a property inside the expression tree -

is there way assign 'result' of selector expression property of selector inside expression tree?

to clarify: i'd transform result set retrieved database data transfer object using selector expression. example this:

expression<func<parent, parentdto>> selector = parent => new parentdto {     children = parent.children.select(x => new childdto())... 

this doesn't work linq entities children (property on entity parent) ienumerable<t> without initializer. case, have static expression accessor (public static expression<func<parent, icollection<child>>> childrenaccessor = f => f.internalchildrenstorage) returns internal collection (icollection<t>). need to:

1. create dto mapping expression child entities
2. create dto mapping expression parent entity (parent entity)
3. replace parameters of static accessor ones child entities mapping expression
4. combine parent mapping expression child entities mapping expression

in end, should (pseudo) this:

expression<func<parent, parentdto>> selector = parent =>     new parentdto {         children = parent.internalchildrenstorage.select(x => new childdto())... 

here's got (realworld code):

// parent = setupgroup // child  = setupmap  expression<func<icollection<setupmap>, ienumerable<setupmapdto>>> transformmapstodto =         maps => maps.select(x => new setupmapdto         {             camera = new setupmapcameradto             {                 id = x.camera.id,                 friendlyname = x.camera.friendlyname             },             display = new setupmapdisplaydto             {                 id = x.display.id,                 friendlyname = x.display.friendlyname             }         }).where(x => x.camera != null); var mapsselector = setupgroup.setupmapsaccessor.combine(transformmapstodto);     expression<func<setupgroup, setupgroupreportdto>> transformgroupstodto = @group          => new setupgroupreportdto {             grouptext   = @group.grouptext,             groupnumber = @group.groupnumber         };  expression<func<setupgroupreportdto, ienumerable<setupmapdto>>> dtomapsselector = dto => dto.setupmaps; var parameterexpression = (parameterexpression) (((memberexpression) (dtomapsselector.body)).expression); var assignment = expression.lambda<action<setupgroupreportdto>>(expression.assign(dtomapsselector.body, mapsselector.body),                     parameterexpression);  var resultdtoblock      = expression.block(transformgroupstodto, assignment);  var selectorparameter   = expression.parameter(typeof (setupgroup)); var dtoselector         = expression.lambda<func<setupgroup, setupgroupreportdto>>(resultdtoblock, selectorparameter);  var results = _setupgrouprepository.getall(dtoselector); 

this doesn't seem work second part of block expression (the assignment) doesn't combined transformgroupstodto expression. did misunderstand purpose of expression.block?