EF Core 3.1如何给IIncludableQueryable添加Tag且不改变其类型？

核心是利用 IIncludableQueryable 本身继承自 IQueryable 的特性，给 ThenInclude 后的查询加标签后强制转换回 IIncludableQueryable 类型即可。EF Core 中 TagWith 仅修改查询表达式树的标签节点，不会改变查询的实际类型结构，强转操作完全安全。
你需要实现两个 ThenIncludeWithHint 重载，分别对应单实体导航属性和集合导航属性的后续关联场景：

using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Query;
using System.Linq.Expressions;

public static class QueryHintsExtensions
{
    // 保留原有其他方法不变，新增以下两个重载

    /// <summary>
    /// 单实体导航属性的ThenInclude带提示重载
    /// </summary>
    public static IIncludableQueryable<TEntity, TProperty> ThenIncludeWithHint<TEntity, TPrevious, TProperty>(
        this IIncludableQueryable<TEntity, TPrevious> source,
        Expression<Func<TPrevious, TProperty>> navigationPropertyPath,
        DbContext context,
        QueryHintsTypes hint,
        string optionalParameter = "")
        where TEntity : class
    {
        var tableName = GetTableName(typeof(TProperty), context);
        var includableQuery = source.ThenInclude(navigationPropertyPath);
        return (IIncludableQueryable<TEntity, TProperty>)includableQuery.AddTag(hint, tableName, optionalParameter);
    }

    /// <summary>
    /// 集合导航属性的ThenInclude带提示重载
    /// </summary>
    public static IIncludableQueryable<TEntity, TProperty> ThenIncludeWithHint<TEntity, TPrevious, TProperty>(
        this IIncludableQueryable<TEntity, IEnumerable<TPrevious>> source,
        Expression<Func<TPrevious, TProperty>> navigationPropertyPath,
        DbContext context,
        QueryHintsTypes hint,
        string optionalParameter = "")
        where TEntity : class
    {
        var tableName = GetTableName(typeof(TProperty), context);
        var includableQuery = source.ThenInclude(navigationPropertyPath);
        return (IIncludableQueryable<TEntity, TProperty>)includableQuery.AddTag(hint, tableName, optionalParameter);
    }
}

效果验证 #

实现后即可直接使用你预期的链式调用写法：

context.Games.AddHint(c, QueryHintsTypes.Forceseek)
             .IncludeWithHint(g => g.Events, c, QueryHintsTypes.Forceseek)
             .ThenIncludeWithHint(e => e.Team, c, QueryHintsTypes.Forceseek)
             .ThenIncludeWithHint(t => t.Players, c, QueryHintsTypes.Forceseek)
             .Where(...);

所有层级的关联表都会正确生成对应标签，原有的拦截器逻辑不需要做任何修改即可正常识别处理。
内容的提问来源于stack exchange，提问作者DorBS