EntityFrameworkCore Linq错误:类型为“Country”的变量“country.Country”从作用域引用，但未定义

Question

EntityFrameworkCore: 1.1.0

我总是会得到一个带有“简单”linq查询的InvalidOperationException，并且不知道原因。它对标签很有效，但对国家不起作用。

我尝试执行以下查询：

var tags = new string[]{"guid1", "guid2"};
var countries = new int[]{1, 2};
var test = _dbContext.Articles
            .Include(a => a.Countries).ThenInclude(c => c.Country)
            .Include(a => a.Tags)
            .Where(article => article.Tags.Any(t => tags.Contains(t.Tag.Id)) &&
                              article.Countries.Any(c2 => countries.Contains(c2.Country.Id)))
           .ToList();

并始终得到以下异常：

变量“c2.Country”类型为“Country”，从范围引用，但未定义为

与下列实体：

public class Article
{
    /// <summary>
    /// Unique ID of the article
    /// </summary>
    [Required]
    public Guid Id { get; set; }

    /// <summary>
    /// Article type
    /// </summary>
    [Required]
    public ArticleTypes Type { get; set; }

    /// <summary>
    /// Gets or sets the article tags.
    /// </summary>
    /// <value>
    /// The article tags.
    /// </value>
    public ICollection<ArticleTag> Tags { get; set; }

    /// <summary>
    /// Gets or sets the countries.
    /// </summary>
    /// <value>
    /// The countries.
    /// </value>
    public ICollection<ArticleCountry> Countries { get; set; }
}

public class ArticleCountry
{
    /// <summary>
    /// Gets or sets the identifier.
    /// </summary>
    /// <value>
    /// The identifier.
    /// </value>
    public Guid Id { get; set; }

    /// <summary>
    /// Gets or sets the country.
    /// </summary>
    /// <value>
    /// The country.
    /// </value>
    public Country Country { get; set; }

    /// <summary>
    /// 
    /// </summary>
    public int Position { get; set; }
}

public class Country
{
    /// <summary>
    /// Gets or sets the identifier.
    /// </summary>
    /// <value>
    /// The identifier.
    /// </value>
    [JsonIgnore]
    public int Id { get; set; }

    /// <summary>
    /// Unique country code
    /// </summary>
    [JsonProperty("key")]
    [Required]
    [StringLength(2)]
    public string Code { get; set; }

    /// <summary>
    /// Country name
    /// </summary>
    [JsonProperty("name")]
    [Required]
    public string Name { get; set; }
}

public class Tag
{
    /// <summary>
    /// Tag unique key
    /// </summary>
    [JsonProperty("key")]
    [Required]
    public Guid Id { get; set; }

    /// <summary>
    /// Tag name
    /// </summary>
    [JsonProperty("name")]
    [Required]
    public string Name { get; set; }
}

public class ArticleTag
{
    /// <summary>
    /// Gets or sets the identifier.
    /// </summary>
    /// <value>
    /// The identifier.
    /// </value>
    [Required]
    public Guid Id { get; set; }

    /// <summary>
    /// Gets or sets the order.
    /// </summary>
    /// <value>
    /// The order.
    /// </value>
    [Required]
    public int Position { get; set; }

    /// <summary>
    /// Gets or sets the tag.
    /// </summary>
    /// <value>
    /// The tag.
    /// </value>
    [Required]
    public Tag Tag { get; set; }
}

我还可以在控制台中看到以下警告：

警告: Microsoft.EntityFrameworkCore.Query.Internal.SqlServerQueryCompilationContextFactory8无法翻译LINQ表达式“{__countries_1 =>包含(转换((？c2.Country.Id？))}”，并将在本地计算。要配置此警告，请使用DbContextOptionsBuilder.ConfigureWarnings API (事件id DbContextOptionsBuilder.ConfigureWarnings)ConfigureWarnings可用于重写DbContext.OnConfiguring方法或在应用程序服务提供程序上使用AddDbContext。

Answer 1

我通过在ArticleCountry.Country属性中添加Required来解决这个问题

public class ArticleCountry
{
   /// <summary>
   /// Gets or sets the identifier.
   /// </summary>
   /// <value>
   /// The identifier.
   /// </value>
   [Required]
   public Guid Id { get; set; }

   /// <summary>
   /// Gets or sets the country.
   /// </summary>
   /// <value>
   /// The country.
   /// </value>
   [Required]
   public Country Country { get; set; }

   /// <summary>
   /// 
   /// </summary>
   public int Position { get; set; }
}

似乎联接不像可空的FK