我想知道 Entity Framework Core 2 代码优先方法中是否有用于唯一约束的数据注释？
在 EF Core 中，您只能在 Fluent API 中使用扩展方法
HasAlternateKey这篇 MS doc 文章 - 备用键（唯一约束） - 将解释如何使用以及存在哪些进一步的可能性。
上面链接中的一个简短示例：
class MyContext : DbContext
{
public DbSet<Car> Cars { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Car>()
.HasAlternateKey(c => c.LicensePlate)
.HasName("AlternateKey_LicensePlate");
}
}
class Car
{
public int CarId { get; set; }
public string LicensePlate { get; set; }
public string Make { get; set; }
public string Model { get; set; }
}
还可以定义一个唯一索引。因此，在EF Core中你可以使用Fluent API的扩展方法
HasIndex[Index]在这篇 MS doc 文章 - 索引 - 您将找到如何使用的更多信息。
这里是一个使用 Fluent API 的唯一索引的示例：
class MyContext : DbContext
{
public DbSet<Blog> Blogs { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Blog>()
.HasIndex(b => b.Url)
.IsUnique();
}
}
public class Blog
{
public int BlogId { get; set; }
public string Url { get; set; }
}
这里是相同的示例，但带有 数据注释：
[Index(nameof(Url), IsUnique = true)]
public class Blog
{
public int BlogId { get; set; }
public string Url { get; set; }
}
更新2021-09-10
更新2021-09-24
更新一下，现在有一个代码优先注释。
[Index(nameof(MyProperty), IsUnique = true)] // using Microsoft.EntityFrameworkCore
public class MyClass
{
[Key, DatabaseGenerated(DatabaseGeneratedOption.None)]
public Guid Id { get; set; }
[StringLength(255), Required]
public string MyProperty { get; set; }
}
我编写了一个 Attribute 类，它允许您装饰 EF Core Entity 类属性以生成唯一键（无需 Fluent API）。
using System;
using System.ComponentModel.DataAnnotations;
/// <summary>
/// Used on an EntityFramework Entity class to mark a property to be used as a Unique Key
/// </summary>
[AttributeUsageAttribute(AttributeTargets.Property, AllowMultiple = true, Inherited = true)]
public class UniqueKeyAttribute : ValidationAttribute
{
/// <summary>
/// Marker attribute for unique key
/// </summary>
/// <param name="groupId">Optional, used to group multiple entity properties together into a combined Unique Key</param>
/// <param name="order">Optional, used to order the entity properties that are part of a combined Unique Key</param>
public UniqueKeyAttribute(string groupId = null, int order = 0)
{
GroupId = groupId;
Order = order;
}
protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
// we simply return success as no actual data validation is needed because this class implements a "marker attribute" for "create a unique index"
return ValidationResult.Success;
}
public string GroupId { get; set; }
public int Order { get; set; }
}
在 DbContext.cs 文件中的 OnModelCreating(modelBuilder) 方法中，添加以下内容：
// Iterate through all EF Entity types
foreach (var entityType in modelBuilder.Model.GetEntityTypes())
{
#region Convert UniqueKeyAttribute on Entities to UniqueKey in DB
var properties = entityType.GetProperties();
if ((properties != null) && (properties.Any()))
{
foreach (var property in properties)
{
var uniqueKeys = GetUniqueKeyAttributes(entityType, property);
if (uniqueKeys != null)
{
foreach (var uniqueKey in uniqueKeys.Where(x => x.Order == 0))
{
// Single column Unique Key
if (String.IsNullOrWhiteSpace(uniqueKey.GroupId))
{
entityType.AddIndex(property).IsUnique = true;
}
// Multiple column Unique Key
else
{
var mutableProperties = new List<IMutableProperty>();
properties.ToList().ForEach(x =>
{
var uks = GetUniqueKeyAttributes(entityType, x);
if (uks != null)
{
foreach (var uk in uks)
{
if ((uk != null) && (uk.GroupId == uniqueKey.GroupId))
{
mutableProperties.Add(x);
}
}
}
});
entityType.AddIndex(mutableProperties).IsUnique = true;
}
}
}
}
}
#endregion Convert UniqueKeyAttribute on Entities to UniqueKey in DB
}
还在您的 DbContext.cs 类中添加此私有方法：
private static IEnumerable<UniqueKeyAttribute> GetUniqueKeyAttributes(IMutableEntityType entityType, IMutableProperty property)
{
if (entityType == null)
{
throw new ArgumentNullException(nameof(entityType));
}
else if (entityType.ClrType == null)
{
throw new ArgumentNullException(nameof(entityType.ClrType));
}
else if (property == null)
{
throw new ArgumentNullException(nameof(property));
}
else if (property.Name == null)
{
throw new ArgumentNullException(nameof(property.Name));
}
var propInfo = entityType.ClrType.GetProperty(
property.Name,
BindingFlags.NonPublic |
BindingFlags.Public |
BindingFlags.Static |
BindingFlags.Instance |
BindingFlags.DeclaredOnly);
if (propInfo == null)
{
return null;
}
return propInfo.GetCustomAttributes<UniqueKeyAttribute>();
}
在 Entity.cs 类中的用法：
public class Company
{
[Required]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public Guid CompanyId { get; set; }
[Required]
[UniqueKey(groupId: "1", order: 0)]
[StringLength(100, MinimumLength = 1)]
public string CompanyName { get; set; }
}
您甚至可以在多个属性中使用它来形成表中多个列的唯一键。 （注意使用“groupId”，然后是“order”）
public class Company
{
[Required]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public Guid CompanyId { get; set; }
[Required]
[UniqueKey(groupId: "1", order: 0)]
[StringLength(100, MinimumLength = 1)]
public string CompanyName { get; set; }
[Required]
[UniqueKey(groupId: "1", order: 1)]
[StringLength(100, MinimumLength = 1)]
public string CompanyLocation { get; set; }
}
我更喜欢对唯一索引进行唯一约束。
大多数数据库管理工具直接在表信息中显示唯一约束，而不仅仅是索引列表。
为了可读性，我也更喜欢注释而不是 Fluent api。
所以我写了自己的自定义类级别AttributeConvention，可以这样使用：
[UniqueConstraint(nameof(Author), nameof(Book), Name = "UQ_Author_Book")]
// name is optional
internal class Books
{
public required string Author { get; set; }
public required string Book { get; set; }
}
实施：
[AttributeUsage(AttributeTargets.Class, AllowMultiple = true)]
public sealed class UniqueConstraintAttribute(params string[] propertyNames) : Attribute
{
private string? _name;
public IReadOnlyList<string> PropertyNames { get; } = [.. propertyNames];
[DisallowNull]
public string? Name
{
get => _name;
set => _name = value;
}
}
public class UniqueConstraintAttributeConvention(ProviderConventionSetBuilderDependencies dependencies) :
TypeAttributeConventionBase<UniqueConstraintAttribute>(dependencies)
{
protected override void ProcessEntityTypeAdded(
IConventionEntityTypeBuilder entityTypeBuilder,
UniqueConstraintAttribute attribute,
IConventionContext<IConventionEntityTypeBuilder> context)
{
var properties = entityTypeBuilder.Metadata.FindProperties(attribute.PropertyNames) ?? [];
if(attribute.PropertyNames.FirstOrDefault(name => !properties.Any(p => p.Name == name)) is string nameNotFound)
throw new Exception($"UniqueConstraint column `{nameNotFound}` can't be found in {entityTypeBuilder.Metadata.Name}");
if (properties.Count == 0)
throw new Exception("No UniqueConstraint columns were set");
if(entityTypeBuilder.HasKey(properties, fromDataAnnotation: true) is IConventionKeyBuilder KeyBuilder &&
attribute.Name is string name)
KeyBuilder.HasName(name);
}
}
现在您必须在 DbContext.ConfigureConventions 回调中添加自定义约定：
internal class DbContext : Microsoft.EntityFrameworkCore.DbContext
{
protected override void ConfigureConventions(ModelConfigurationBuilder configurationBuilder)
{
configurationBuilder.Conventions.Add(sp => new UniqueConstraintAttributeConvention(
sp.GetRequiredService<ProviderConventionSetBuilderDependencies>()));
}
ConfigureConventionsIConventionEntityTypeBuilderHasAlternateKeyHasKey()在
DbContext.csOnModelCreating(modelBuilder)ForEach.OrderBy(o => o.Order)