RestKit 0.20.1 复合键和嵌套关系

Posted 2023-03-05

【中文标题】RestKit 0.20.1 复合键和嵌套关系

【英文标题】：RestKit 0.20.1 Composite keys and nested relationships

【发布时间】：2013-05-31 13:16:01

【问题描述】：

我正在使用 RestKit 0.20.1 将 XML 提要映射到核心数据模型。它们如下：

XML 提要

<?xml version="1.0" encoding="utf-8"?>
<payload>
    <competitions>
        <competition id="100" name="Comp A" />
        <competition id="200" name="Comp B" />
        <competition id="300" name="Comp C" />
        <competition id="400" name="Comp D" />
    </competitions>
    <seasons>
        <season id="10" span="2008/09"/>
        <season id="20" span="2009/10"/>
        <season id="30" span="2010/11"/>
        <season id="40" span="2011/12"/>
        <season id="50" span="2012/13"/>
    </seasons>
    <players>
        <player id="1" name="Justyn Spooner">
            <season id="10">
                <playerstats competitionID="100" goals="0" played="0" />
                <playerstats competitionID="200" goals="5" played="4" />
                <playerstats competitionID="300" goals="2" played="1" />
            </season>
            <season id="20">
                <playerstats competitionID="300" goals="1" played="4" />
                <playerstats competitionID="400" goals="2" played="9" />
            </season>
        </player>
    </players>
</payload>

核心数据模型

到目前为止，我已经设置了实体映射和响应描述符，但不确定如何设置它们之间的关系。

实体映射

RKEntityMapping *playerMapping = [RKEntityMapping mappingForEntityForName:@"Player" inManagedObjectStore:[[RKObjectManager sharedManager] managedObjectStore]];
playerMapping.identificationAttributes = @[@"attID"];
[playerMapping addAttributeMappingsFromDictionary:@
    @"id"   : @"attID",
    @"name" : @"attName"
];

RKEntityMapping *competitionMapping = [RKEntityMapping mappingForEntityForName:@"Competition" inManagedObjectStore:[[RKObjectManager sharedManager] managedObjectStore]];
competitionMapping.identificationAttributes = @[@"attID"];
[competitionMapping addAttributeMappingsFromDictionary:@
    @"id"   : @"attID",
    @"name" : @"attName"
];

RKEntityMapping *seasonMapping = [RKEntityMapping mappingForEntityForName:@"Season" inManagedObjectStore:[[RKObjectManager sharedManager] managedObjectStore]];
seasonMapping.identificationAttributes = @[@"attID"];
[seasonMapping addAttributeMappingsFromDictionary:@
    @"id"   : @"attID",
    @"span" : @"attYearSpan"
];

RKEntityMapping *playerStatsMapping = [RKEntityMapping mappingForEntityForName:@"PlayerStats" inManagedObjectStore:[[RKObjectManager sharedManager] managedObjectStore]];
playerStatsMapping.identificationAttributes = @[@"attFKCompetitionID", @"attFKSeasonID", @"attFKPlayerID"];
[playerStatsMapping addAttributeMappingsFromDictionary:@
    @"competitionID" : @"attFKCompetitionID",
    @"????"          : @"attFKSeasonID",
    @"????"          : @"attFKPlayerID",
    @"goals"         : @"attGoals",
    @"played"        : @"attGamesPlayed"
];

响应描述符

RKResponseDescriptor *playerResponseDescriptor =        [RKResponseDescriptor responseDescriptorWithMapping:playerMapping       pathPattern:kURLBasePath@"/players" keyPath:@"payload.players.player"                       statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)];
RKResponseDescriptor *seasonResponseDescriptor =        [RKResponseDescriptor responseDescriptorWithMapping:seasonMapping       pathPattern:kURLBasePath@"/players" keyPath:@"payload.seasons.season"                       statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)];
RKResponseDescriptor *competitionResponseDescriptor =   [RKResponseDescriptor responseDescriptorWithMapping:competitionMapping  pathPattern:kURLBasePath@"/players" keyPath:@"payload.competitions.competition"             statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)];
RKResponseDescriptor *playerStatsResponseDescriptor =   [RKResponseDescriptor responseDescriptorWithMapping:playerStatsMapping  pathPattern:kURLBasePath@"/players" keyPath:@"payload.players.player.season.playerstats"    statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)];

除了缺少的关系之外，您会注意到在 playerStatsMapping 中我需要添加一个由 Player、Season 和 Competition 三个主键组成的 IdentificationAttribute。比赛 ID 很容易映射，因为它直接位于 keyPath payload.players.player.season.playerstats（在 playerStatsResponseDescriptor 中定义）下。问题是我不知道如何引用playerStatMapping中的parent.id和parent.parent.id分别映射到attFKSeasonID和attFKPlayerID。

我不认为 RestKit 支持访问 entityMappings 中的父 keyPath，我确定可能有另一种解决方法？这张图显示了我想要提取的内容：

在伪代码中，如果我不使用 RestKit，这就是我想要做的：

For each player in the XML response:

    find out if that player exists in Core Data; create if not
    keep it around in a local variable
    for each season under the player in the XML:
    
        create if needed; keep around.
        for each competition under the season in the XML:
        
            create if needed; keep around.
            Take the current player, season and competition. 
            Is there a PlayerStat matching those three things? Create if not
            Set that player stat's attGoals and attGamesPlayed to the values that are mapped from goals and played in the XML
        
    

所以这里基本上有两个问题：

您将如何设置关系映射？ 在构造playerStatsMapping 时如何映射player 和season id，以便playerStatsMapping 可以将它们用作identificationAttributes？

任何帮助将不胜感激。

谢谢， 贾斯汀

【问题讨论】：

一旦建立了关系，你真的需要ID吗？使用关系，您可以导航到关系目标对象的统计信息或谓词搜索。这对你有用吗？

@Wain 感谢您的快速回复。关系可能会解决它。我已经更新了问题以使其更清楚。我目前无法识别个人playerstat，因为它没有自己的 ID。我希望从它引用的比赛及其父母（球员和赛季）中产生这个。这三个组合键应该允许为 playerStats 条目创建唯一键。我这样做是因为我认为 RestKit 需要一个映射来设置一个 IdentificationAttribute 以便它能够检测和更新现有条目而不是创建一个新条目？

没错，identificationAttribute 很重要。标识的最佳选择可能是在托管对象子类中实现“willSave”，并通过询问关系在其中生成值。我认为在映射过程中没有办法向后导航。可能是在映射过程中尝试编辑映射变量（我之前没有尝试过）。

好的，我会继续玩它，如果我知道如何做到这一点，我会回帖。如果没有其他方法，“willSave”选项可能是一个很好的后备方案。谢谢。

我可能应该将其拆分为单独的问题，但您将如何为该映射创建关系？

【参考方案1】：

简而言之，RestKit 现在支持 @parent 和 @root 映射键作为 development branch 的一部分。这允许访问当前映射对象的父节点，如果它被映射为其父实体的关系。

这和我遇到的另一个问题非常相似，如果需要，我可以更详细地提供上述具体案例的答案，否则请查看this answer。