可以使用LINQKit将表达式树注入到过滤器中，需要配置DbContextOptions：

builder
    .UseSqlServer(connectionString) // or any other provider
    .WithExpressionExpanding();     // enabling LINQKit extension

您的类应该使用返回Expression<Func<>>的静态函数进行扩展，当前方法应该具有ExpandableAttribute
例如：

public class Gym
{
    [Expandable(nameof(IsAppreciateToRequestImpl))]
    public bool IsAppreciateToRequest(GetGymRequest other)
    {
        return (string.IsNullOrEmpty(other.Name) || Name == other.Name)
                && (string.IsNullOrEmpty(other.Location) || Location == other.Location) 
                && (other.SectionRequest == null || Sections.All(section => section.IsAppreciateToRequest(other.SectionRequest)));
    }

    private static Expression<Func<Gym, GetGymRequest, bool>> IsAppreciateToRequestImpl()
    {
        // first parameter is current object
        return (gym, other) => (string.IsNullOrEmpty(other.Name) || gym.Name == other.Name)
                && (string.IsNullOrEmpty(other.Location) || gym.Location == other.Location) 
                && (other.SectionRequest == null || gym.Sections.All(section => section.IsAppreciateToRequest(other.SectionRequest)));
    }
}

// the same technique as in Gym class
public class Section
{
    [Expandable(nameof(IsAppreciateToRequestImpl))]
    public bool IsAppreciateToRequest(GetSectionRequest other)
    {
        return // unknown;
    }

    private static Expression<Func<Section, GetSectionRequest, bool>> IsAppreciateToRequestImpl()
    {
        // first parameter is current object
        return (section, other) => // unknown;
    }
}

然后LINQKit将扩展静态方法返回的表达式，并将条件注入 predicate 。
同样的方法可以用于将实体投影到DTO。类似于我的答案here，它也显示了LINQKit的已知替代方案。