ios - How to multiply two columns and sum it in CoreData? -

i have goods in document , want multiply quantity , price of every in document , sum it.

in mysql this: select sum(price * quantity) documentgoods

here code, doesn't work.

nsfetchrequest *fetch = [[nsfetchrequest alloc] init]; [fetch setentity:[nsentitydescription entityforname:self.tablename inmanagedobjectcontext:moc]]; [fetch setresulttype:nsdictionaryresulttype];  nsexpression *multiplyexpression = [nsexpression expressionforfunction:@"multiply:by:" arguments:@[[nsexpression expressionforkeypath:@"quantity"], [nsexpression expressionforkeypath:@"price"]]]; nsexpressiondescription *expressionmultiplieddescription = [[nsexpressiondescription alloc] init]; [expressionmultiplieddescription setname:@"multiplied"]; [expressionmultiplieddescription setexpression:multiplyexpression]; [expressionmultiplieddescription setexpressionresulttype:nsdecimalattributetype];  nsexpression *sumexpression = [nsexpression expressionforfunction:@"sum:" arguments:@[[nsexpression expressionforkeypath:@"multiplied"]]]; nsexpressiondescription *expressionsummarydescription = [[nsexpressiondescription alloc] init]; [expressionsummarydescription setname:@"summary"]; [expressionsummarydescription setexpression:sumexpression]; [expressionsummarydescription setexpressionresulttype:nsdecimalattributetype];  [fetch setpropertiestofetch:@[expressionsummarydescription]]; nspredicate *searchfilter = [nscompoundpredicate andpredicatewithsubpredicates:@[[nspredicate predicatewithformat:@"removed = no"]]]; [fetch setpredicate:searchfilter]; nserror *error = nil; nsarray *objects = [moc executefetchrequest:fetch error:&error]; if(objects && [objects count] > 0)     return [[objects objectatindex:0] valueforkey:@"summary"]; return [[nsdecimalnumber alloc] initwithfloat:.0f]; 

can please me?

i faced similar scenario entity "cart" , has fields price , quantity. sum(quantity * price) cart used following code. last nslog log required total cart price

nsfetchrequest *request = [[nsfetchrequest alloc] init];  request.entity = [nsentitydescription entityforname:@"cart" inmanagedobjectcontext:self.managedobjectcontext]; request.resulttype = nsdictionaryresulttype;  nsexpressiondescription *producttotaldescr = [[nsexpressiondescription alloc] init]; [producttotaldescr setname:@"producttotal"]; [producttotaldescr setexpression:[nsexpression expressionforfunction:@"multiply:by:"                                                     arguments:[nsarray arraywithobjects:                                                                [nsexpression expressionforkeypath:@"price"],                                                                [nsexpression expressionforkeypath:@"quantity"],                                                                nil]]]; [producttotaldescr setexpressionresulttype:nsinteger64attributetype];  request.propertiestofetch = [nsarray arraywithobjects:producttotaldescr, nil];  nserror *err = nil; nsarray *results = [self.managedobjectcontext executefetchrequest:request error:&err]; nslog(@"%@",[results valueforkeypath:@"producttotal"]);