CoreData常用的查询

总结下CoreData常用的一些查询

fetchLimit和fetchOffset分页查询、多字段排序：

-(NSArray *)sc_conversationWithParentId:(NSString *)parentId page:(int)page{
    
    static int limit=20;
    NSFetchRequest *request=[NSFetchRequest fetchRequestWithEntityName:@"SCConversation"];
    request.fetchLimit=limit;
    request.fetchOffset=(page-1)*limit;
    NSPredicate *predicate=[NSPredicate predicateWithFormat:@"parentId=%@ and (content.length>0 or draft.length>0) and type in {0,1,3,5}",parentId];
    request.predicate=predicate;
    
    NSSortDescriptor *topSorter=[NSSortDescriptor sortDescriptorWithKey:@"topNo" ascending:NO];
    NSSortDescriptor *timeSorter=[NSSortDescriptor sortDescriptorWithKey:@"time" ascending:NO];

    request.sortDescriptors=@[topSorter,timeSorter];
    
    NSArray *array=[self.ctxt executeFetchRequest:request error:nil];
    if(array.count==0){
        
        return nil;
    }
    return array;
}

NSExpressionDescription对某个字段求和：

-(NSInteger)totalUnreadCountInNodeName:(NSString *)nodeName{
    
    NSFetchRequest *request=[NSFetchRequest fetchRequestWithEntityName:@"SCConversation"];
    
    request.resultType=NSDictionaryResultType;
    
    NSExpressionDescription *expressionDescription=[[NSExpressionDescription alloc] init];
    
    NSExpression *expression=[NSExpression expressionWithFormat:@"@sum.unreadCount"];
    
    expressionDescription.expression=expression;
    expressionDescription.expressionResultType=NSInteger64AttributeType;
    expressionDescription.name=@"total";
    
    request.propertiesToFetch=@[expressionDescription];
    
    NSPredicate *predicate=[NSPredicate predicateWithFormat:@"parentId=%@",nodeName];
    request.predicate=predicate;
    
    NSArray *array=[self.ctxt executeFetchRequest:request error:nil];
    if(!array || array.count==0){
        
        return 0;
    }
    NSDictionary *dict=[array lastObject];
    return (NSInteger)[[dict objectForKey:@"total"] integerValue];
}

带时间截的查询:

-(NSArray *)sc_messageWithConversationId:(NSString *)conversationId page:(int)page timestop:(NSDate *)timestop{
    
    if(!conversationId || conversationId.length==0){
        
        return nil;
    }
    static int messagePageCount=20;
    NSFetchRequest *request=[NSFetchRequest fetchRequestWithEntityName:@"SCMessage"];
    NSPredicate *predicate=[NSPredicate predicateWithFormat:@"conversationId=%@ and time<=%@",conversationId,timestop];
    request.predicate=predicate;
    
    request.fetchOffset=(page-1)*messagePageCount;
    request.fetchLimit=messagePageCount;
    
    NSSortDescriptor *sorter=[NSSortDescriptor sortDescriptorWithKey:@"time" ascending:NO];
    request.sortDescriptors=@[sorter];
    
    NSArray *array=[self.ctxt executeFetchRequest:request error:nil];
    if(array.count==0){
        
        return nil;
    }
    return array;
}

多个查询条件:

-(NSArray *)sc_messageWithConversationId:(NSString *)conversationId userId:(NSString *)userId userNo:(uint64_t)userNo{
    
    if(!conversationId || conversationId.length==0){
        
        return nil;
    }
    NSFetchRequest *request=[NSFetchRequest fetchRequestWithEntityName:@"SCMessage"];
    NSPredicate *predicate=[NSPredicate predicateWithFormat:@"conversationId=%@ and userId=%@ and userNo=%lld",conversationId,userId,userNo];
    request.predicate=predicate;
    NSArray *array=[self.ctxt executeFetchRequest:request error:nil];
    if(array.count==0){
        
        return nil;
    }
    return array;
}