使用Azure AI Search索引投影提取PDF单页内容遇报错求助

需使用Azure AI Search返回PDF文档中匹配搜索查询的特定页面。当前通过generateNormalizedImagePerPage将PDF每页转为图片，再用OcrSkill提取文本，虽能拆分内容，但查询索引时返回的是整个PDF文档，而非匹配的单页。

尝试通过索引投影将PDF每页作为搜索索引中的独立文档，创建索引及投影配置后，创建技能集时触发报错：

One or more index projection selectors are invalid. 
Details: Index 'myindex' must contain field 'content', it must be of type Edm.String, 
cannot be the key field and it must be filterable.

用户的索引定义代码：

var index = new SearchIndex(name: "myindex")
{
    Fields =
    [
        new SearchField (name: "id", type: SearchFieldDataType.String) 
            { IsSearchable = true, IsKey = true, },
        new SearchField (name: "content", type: SearchFieldDataType.String) 
            { IsFilterable = true, IsKey = false },
        new SearchField (name: "pagetext", type: SearchFieldDataType.String) 
            { IsSearchable = true },
        new SearchField (name: "pagenumber", type: SearchFieldDataType.String) 
            { IsSearchable = true }
    ]
};

用户的索引投影配置代码：

var mappings = new List<InputFieldMappingEntry>
{
    new (name: "pagetext")
    {
        Source = "/document/normalized_images/*/text"
    },
    new (name: "pagenumber")
    {
        Source = "/document/normalized_images/*/pageNumber"
    }
};

var selectors = new List<SearchIndexerIndexProjectionSelector>
{
    new (targetIndexName: "myindex",
         parentKeyFieldName: "content",
         sourceContext: "/document/normalized_images/*",
         mappings: mappings)
};

var indexProjections = new SearchIndexerIndexProjections(selectors)
{
    Parameters = new SearchIndexerIndexProjectionsParameters
    {
        ProjectionMode = IndexProjectionMode.SkipIndexingParentDocuments
    }
};

报错核心原因是：索引投影的parentKeyFieldName指定了content字段，但投影配置中未将父文档的对应字段映射到子文档的content字段，导致系统检测不到该字段的有效赋值逻辑，触发校验报错。

具体修正步骤：

1. 补充content字段的投影映射
   在投影字段映射列表中添加content字段的映射，将父文档的content字段（原始PDF的标识字段）传递给子文档：

   var mappings = new List<InputFieldMappingEntry>
   {
       new (name: "pagetext")
       {
           Source = "/document/normalized_images/*/text"
       },
       new (name: "pagenumber")
       {
           Source = "/document/normalized_images/*/pageNumber"
       },
       // 新增：将父文档的content字段映射到子文档的content字段
       new (name: "content")
       {
           Source = "/document/content"
       }
   };
   

2. 确保父文档content字段可被提取
   确认索引器配置中已开启原始PDF的文本提取功能，保证父文档的content字段能正常获取到值（可通过内置的PDF解析能力实现）。
3. 优化pagenumber字段类型（可选）
   将pagenumber字段类型改为Int32，更便于后续筛选、排序操作，修改后的索引字段定义：

   new SearchField (name: "pagenumber", type: SearchFieldDataType.Int32) 
       { IsFilterable = true, IsSortable = true }
   

内容的提问来源于stack exchange，提问作者Tyloo