Entity Framework迁移中必填字段的默认值？

Question

我已将[Required]数据注释添加到ASP.NET MVC application中的一个模型中。创建迁移后，运行Update-Database命令会导致以下错误：

无法将值NULL插入列'Director'，表'MOVIES_cf7bad808fa94f89afa2e5dae1161e78.dbo.Movies';列不允许空值。更新失败。该语句已终止。

这是因为一些记录在Director列中有NULL。如何自动将这些值更改为默认值（例如“John Doe”）导演？

这是我的模型：

  public class Movie
    {
        public int ID { get; set; }
        [Required]
        public string Title { get; set; }

        [DataType(DataType.Date)]
        public DateTime ReleaseDate { get; set; }

        [Required]
        public string Genre { get; set; }

        [Range(1,100)]
        [DataType(DataType.Currency)]
        public decimal Price { get; set; }

        [StringLength(5)]
        public string Rating { get; set; }

        [Required]     /// <--- NEW
        public string Director { get; set; }
    }

这是我最近的迁移：

public partial class AddDataAnnotationsMig : DbMigration
{
    public override void Up()
    {
        AlterColumn("dbo.Movies", "Title", c => c.String(nullable: false));
        AlterColumn("dbo.Movies", "Genre", c => c.String(nullable: false));
        AlterColumn("dbo.Movies", "Rating", c => c.String(maxLength: 5));
        AlterColumn("dbo.Movies", "Director", c => c.String(nullable: false));
    }

    public override void Down()
    {
        AlterColumn("dbo.Movies", "Director", c => c.String());
        AlterColumn("dbo.Movies", "Rating", c => c.String());
        AlterColumn("dbo.Movies", "Genre", c => c.String());
        AlterColumn("dbo.Movies", "Title", c => c.String());
    }
}

Answer 1

如果我没记错的话，这样的事情应该有效：

AlterColumn("dbo.Movies", "Director", c => c.String(nullable: false, defaultValueSql: "John Doe"));

Answer 2

除了@webdeveloper和@Pushpendra的答案之外，您还需要手动向迁移添加更新以更新现有行。例如：

public override void Up()
{
    Sql("UPDATE [dbo].[Movies] SET Title = 'No Title' WHERE Title IS NULL");
    AlterColumn("dbo.Movies", "Title", c => c.String(nullable: false,defaultValue:"MyTitle"));
}

这是因为AlterColumn生成DDL以将列的默认值设置为表规范中的某个特定值。 DDL不会影响数据库中的现有行。

你实际上是在同一时间进行两次更改（设置默认值并使列为NOT NULL），并且每个更改都是单独有效的，但由于你是同时制作两个，所以你可以期望系统'智能地'实现你的意图并将所有NULL值设置为默认值，但这不是所期望的。

假设您只设置列的默认值，而不是使其为NOT NULL。您显然不希望使用您提供的默认值更新所有NULL记录。

因此，在我看来，这不是一个错误，我不希望EF以我没有明确告诉它的方式更新我的数据。开发人员负责指示系统如何处理数据。

Answer 3

public partial class AddDataAnnotationsMig : DbMigration
{
    public override void Up()
    {
        AlterColumn("dbo.Movies", "Title", c => c.String(nullable: false,defaultValue:"MyTitle"));
        AlterColumn("dbo.Movies", "Genre", c => c.String(nullable: false,defaultValue:"Genre"));
        AlterColumn("dbo.Movies", "Rating", c => c.String(maxLength: 5));
        AlterColumn("dbo.Movies", "Director", c => c.String(nullable: false,defaultValue:"Director"));

    }

    public override void Down()
    {       
        AlterColumn("dbo.Movies", "Director", c => c.String());
        AlterColumn("dbo.Movies", "Rating", c => c.String());
        AlterColumn("dbo.Movies", "Genre", c => c.String());
        AlterColumn("dbo.Movies", "Title", c => c.String());       
    }
}

Answer 4

不确定这个选项是否总是存在但只是遇到了类似的问题，发现我能够设置默认值而不使用以下运行任何手动更新

defaultValueSql: "'NY'"

当提供的值是"NY"时我得到了一个错误然后我意识到他们期待像"GETDATE()"这样的SQL值所以我尝试了"'NY'"并且这样做了

整条线看起来像这样

AddColumn("TABLE_NAME", "State", c => c.String(maxLength: 2, nullable: false, defaultValueSql: "'NY'"));

感谢this answer，让我走上正轨

Answer 5

我发现只在实体属性上使用Auto-Property Initializer就足以完成工作。

例如：

public class Thing {
    public bool IsBigThing { get; set; } = false;
}

Answer 6

出于某种原因，我无法解释自己批准的答案对我来说不再适用。

它适用于另一个应用程序，在我工作的应用程序上没有。

因此，另一种但非常低效的解决方案是覆盖SaveChanges（）方法，如下所示。此方法应该在Context类上。

    public override int SaveChanges()
    {
        foreach (var entry in ChangeTracker.Entries().Where(entry => entry.Entity.GetType().GetProperty("ColumnName") != null))
        {
            if (entry.State == EntityState.Added)
            {
                entry.Property("ColumnName").CurrentValue = "DefaultValue";
            }
        }

Answer 7

许多其他响应都集中在如何在发生这些问题时手动干预。

生成迁移后，请对迁移执行以下任一更改：

修改Column定义以包含defaultValue或defaultSql语句： AlterColumn("dbo.Movies", "Director", c => c.String(nullable: false, default: ""));

在AlterColumn之前注入一个SQL语句以预填充现有列： Sql("UPDATE dbo.Movies SET Director = '' WHERE Director IS NULL");

请记住，如果重新构建迁移，将覆盖应用于迁移脚本的手动更改。对于第一个解决方案，扩展EF非常容易，可以在迁移生成过程中自动定义字段的默认值。

注意：EF不会自动为您执行此操作，因为每个RDBMS提供程序的默认值实现会有所不同，但也因为默认值在纯EF运行时中的含义较少，因为每个行插入将为每个属性提供当前值，即使它为null，也永远不会计算默认值约束。这个AlterColumn语句是默认约束发挥作用的唯一时间，我想这对于设计SQL Server迁移实现的团队来说是一个较低的优先级。

以下解决方案结合了属性表示法，模型配置约定和列注释，以将元数据传递给自定义迁移代码生成器。如果您不使用属性表示法，则可以使用每个受影响字段的流利表示法替换步骤1和2。这里有很多技巧，随意使用部分或全部，我希望这里的每个人都有价值

声明默认值创建或重新定义现有属性以定义要使用的默认值，对于此示例，我们将创建一个名为DefaultValue的新属性，该属性继承自ComponentModel.DefaultValueAttribute，因为使用是直观的，并且现有代码库有可能已实现这个属性。使用此实现，您只需使用此特定属性来访问DefaultValueSql，这对日期和其他自定义方案很有用。履行 [DefaultValue("Insert DefaultValue Here")] [Required] /// <--- NEW public string Director { get; set; } // Example of default value sql [DefaultValue(DefaultValueSql: "GetDate()")] [Required] public string LastModified { get; set; } Attrribute定义 namespace EFExtensions { /// <summary> /// Specifies the default value for a property but allows a custom SQL statement to be provided as well. <see cref="MiniTuber.Database.Conventions.DefaultValueConvention"/> /// </summary> public class DefaultValueAttribute : System.ComponentModel.DefaultValueAttribute { /// <summary> /// Specifies the default value for a property but allows a custom SQL statement to be provided as well. <see cref="MiniTuber.Database.Conventions.DefaultValueConvention"/> /// </summary> public DefaultValueAttribute() : base("") { } /// <i /// <summary> /// Optional SQL to use to specify the default value. /// </summary> public string DefaultSql { get; set; } /// <summary> /// Initializes a new instance of the System.ComponentModel.DefaultValueAttribute /// class using a Unicode character. /// </summary> /// <param name="value"> /// A Unicode character that is the default value. /// </param> public DefaultValueAttribute(char value) : base(value) { } /// <summary> /// Initializes a new instance of the System.ComponentModel.DefaultValueAttribute /// class using an 8-bit unsigned integer. /// </summary> /// <param name="value"> /// An 8-bit unsigned integer that is the default value. /// </param> public DefaultValueAttribute(byte value) : base(value) { } /// <summary> /// Initializes a new instance of the System.ComponentModel.DefaultValueAttribute /// class using a 16-bit signed integer. /// </summary> /// <param name="value"> /// A 16-bit signed integer that is the default value. /// </param> public DefaultValueAttribute(short value) : base(value) { } /// <summary> /// Initializes a new instance of the System.ComponentModel.DefaultValueAttribute /// class using a 32-bit signed integer. /// </summary> /// <param name="value"> /// A 32-bit signed integer that is the default value. /// </param> public DefaultValueAttribute(int value) : base(value) { } /// <summary> /// Initializes a new instance of the System.ComponentModel.DefaultValueAttribute /// class using a 64-bit signed integer. /// </summary> /// <param name="value"> /// A 64-bit signed integer that is the default value. /// </param> public DefaultValueAttribute(long value) : base(value) { } /// <summary> /// Initializes a new instance of the System.ComponentModel.DefaultValueAttribute /// class using a single-precision floating point number. /// </summary> /// <param name="value"> /// A single-precision floating point number that is the default value. /// </param> public DefaultValueAttribute(float value) : base(value) { } /// <summary> /// Initializes a new instance of the System.ComponentModel.DefaultValueAttribute /// class using a double-precision floating point number. /// </summary> /// <param name="value"> /// A double-precision floating point number that is the default value. /// </param> public DefaultValueAttribute(double value) : base(value) { } /// <summary> /// Initializes a new instance of the System.ComponentModel.DefaultValueAttribute /// class using a System.Boolean value. /// </summary> /// <param name="value"> /// A System.Boolean that is the default value. /// </param> public DefaultValueAttribute(bool value) : base(value) { } /// <summary> /// Initializes a new instance of the System.ComponentModel.DefaultValueAttribute /// class using a System.String. /// </summary> /// <param name="value"> /// A System.String that is the default value. /// </param> public DefaultValueAttribute(string value) : base(value) { } /// <summary> /// Initializes a new instance of the System.ComponentModel.DefaultValueAttribute /// class. /// </summary> /// <param name="value"> /// An System.Object that represents the default value. /// </param> public DefaultValueAttribute(object value) : base(value) { } /// /// <inheritdoc/> /// Initializes a new instance of the System.ComponentModel.DefaultValueAttribute /// class, converting the specified value to the specified type, and using an invariant /// culture as the translation context. /// </summary> /// <param name="type"> /// A System.Type that represents the type to convert the value to. /// </param> /// <param name="value"> /// A System.String that can be converted to the type using the System.ComponentModel.TypeConverter /// for the type and the U.S. English culture. /// </param> public DefaultValueAttribute(Type type, string value) : base(value) { } } }
创建一个约定以将默认值注入列注释列注释用于将有关列的自定义元数据传递到迁移脚本生成器。使用约定来演示属性表示法背后的能力，以简化如何为许多属性定义和操作流畅的元数据，而不是为每个字段单独指定它。 namespace EFExtensions { /// <summary> /// Implement SQL Default Values from System.ComponentModel.DefaultValueAttribute /// </summary> public class DefaultValueConvention : Convention { /// <summary> /// Annotation Key to use for Default Values specified directly as an object /// </summary> public const string DirectValueAnnotationKey = "DefaultValue"; /// <summary> /// Annotation Key to use for Default Values specified as SQL Strings /// </summary> public const string SqlValueAnnotationKey = "DefaultSql"; /// <summary> /// Implement SQL Default Values from System.ComponentModel.DefaultValueAttribute /// </summary> public DefaultValueConvention() { // Implement SO Default Value Attributes first this.Properties() .Where(x => x.HasAttribute<EFExtensions.DefaultValueAttribute>()) .Configure(c => c.HasColumnAnnotation( c.GetAttribute<EFExtensions.DefaultValueAttribute>().GetDefaultValueAttributeKey(), c.GetAttribute<EFExtensions.DefaultValueAttribute>().GetDefaultValueAttributeValue() )); // Implement Component Model Default Value Attributes, but only if it is not the SO implementation this.Properties() .Where(x => x.HasAttribute<System.ComponentModel.DefaultValueAttribute>()) .Where(x => !x.HasAttribute<MiniTuber.DataAnnotations.DefaultValueAttribute>()) .Configure(c => c.HasColumnAnnotation( DefaultValueConvention.DirectValueAnnotationKey, c.GetAttribute<System.ComponentModel.DefaultValueAttribute>().Value )); } } /// <summary> /// Extension Methods to simplify the logic for building column annotations for Default Value processing /// </summary> public static partial class PropertyInfoAttributeExtensions { /// <summary> /// Wrapper to simplify the lookup for a specific attribute on a property info. /// </summary> /// <typeparam name="T">Type of attribute to lookup</typeparam> /// <param name="self">PropertyInfo to inspect</param> /// <returns>True if an attribute of the requested type exists</returns> public static bool HasAttribute<T>(this PropertyInfo self) where T : Attribute { return self.GetCustomAttributes(false).OfType<T>().Any(); } /// <summary> /// Wrapper to return the first attribute of the specified type /// </summary> /// <typeparam name="T">Type of attribute to return</typeparam> /// <param name="self">PropertyInfo to inspect</param> /// <returns>First attribuite that matches the requested type</returns> public static T GetAttribute<T>(this System.Data.Entity.ModelConfiguration.Configuration.ConventionPrimitivePropertyConfiguration self) where T : Attribute { return self.ClrPropertyInfo.GetCustomAttributes(false).OfType<T>().First(); } /// <summary> /// Helper to select the correct DefaultValue annotation key based on the attribute values /// </summary> /// <param name="self"></param> /// <returns></returns> public static string GetDefaultValueAttributeKey(this EFExtensions.DefaultValueAttribute self) { return String.IsNullOrWhiteSpace(self.DefaultSql) ? DefaultValueConvention.DirectValueAnnotationKey : DefaultValueConvention.SqlValueAnnotationKey; } /// <summary> /// Helper to select the correct attribute property to send as a DefaultValue annotation value /// </summary> /// <param name="self"></param> /// <returns></returns> public static object GetDefaultValueAttributeValue(this EFExtensions.DefaultValueAttribute self) { return String.IsNullOrWhiteSpace(self.DefaultSql) ? self.Value : self.DefaultSql; } } }
将“公约”添加到DbContext 有很多方法可以实现这一点，我喜欢将约定声明为我的ModelCreation逻辑中的第一个自定义步骤，这将在您的DbContext类中。 protected override void OnModelCreating(DbModelBuilder modelBuilder) { base.OnModelCreating(modelBuilder); // Use our new DefaultValueConvention modelBuilder.Conventions.Add<EFExtensions.DefaultValueConvention>(); // My personal favourites ;) modelBuilder.Conventions.Remove<PluralizingTableNameConvention>(); modelBuilder.Conventions.Remove<OneToManyCascadeDeleteConvention>(); }
覆盖MigrationCodeGenerator 现在这些注释已应用于模型中的列定义，我们需要修改迁移脚本生成器以使用这些注释。为此，我们将继承System.Data.Entity.Migrations.Design.CSharpMigrationCodeGenerator，因为我们只需要注入最少量的更改。处理完我们的自定义注释后，我们需要将其从列定义中删除，以防止它被序列化为最终输出。请参阅基类代码以探索其他用法：http://entityframework.codeplex.com/sourcecontrol/latest#src/EntityFramework/Migrations/Design/CSharpMigrationCodeGenerator.cs namespace EFExtensions { /// <summary> /// Implement DefaultValue constraint definition in Migration Scripts. /// </summary> /// <remarks> /// Original guide that provided inspiration for this https://romiller.com/2012/11/30/code-first-migrations-customizing-scaffolded-code/ /// </remarks> public class CustomCodeGenerator : System.Data.Entity.Migrations.Design.CSharpMigrationCodeGenerator { /// <summary> /// Inject Default values from the DefaultValue attribute, if the DefaultValueConvention has been enabled. /// </summary> /// <seealso cref="DefaultValueConvention"/> /// <param name="column"></param> /// <param name="writer"></param> /// <param name="emitName"></param> protected override void Generate(ColumnModel column, IndentedTextWriter writer, bool emitName = false) { var annotations = column.Annotations?.ToList(); if (annotations != null && annotations.Any()) { for (int index = 0; index < annotations.Count; index ++) { var annotation = annotations[index]; bool handled = true; try { switch (annotation.Key) { case DefaultValueConvention.SqlValueAnnotationKey: if (annotation.Value?.NewValue != null) { column.DefaultValueSql = $"{annotation.Value.NewValue}"; } break; case DefaultValueConvention.DirectValueAnnotationKey: if (annotation.Value?.NewValue != null) { column.DefaultValue = Convert.ChangeType(annotation.Value.NewValue, column.ClrType); } break; default: handled = false; break; } } catch(Exception ex) { // re-throw with specific debug information throw new ApplicationException($"Failed to Implement Column Annotation for column: {column.Name} with key: {annotation.Key} and new value: {annotation.Value.NewValue}", ex); } if(handled) { // remove the annotation, it has been applied column.Annotations.Remove(annotation.Key); } } } base.Generate(column, writer, emitName); } /// <summary> /// Generates class summary comments and default attributes /// </summary> /// <param name="writer"> Text writer to add the generated code to. </param> /// <param name="designer"> A value indicating if this class is being generated for a code-behind file. </param> protected override void WriteClassAttributes(IndentedTextWriter writer, bool designer) { writer.WriteLine("/// <summary>"); writer.WriteLine("/// Definition of the Migration: {0}", this.ClassName); writer.WriteLine("/// </summary>"); writer.WriteLine("/// <remarks>"); writer.WriteLine("/// Generated Time: {0}", DateTime.Now); writer.WriteLine("/// Generated By: {0}", Environment.UserName); writer.WriteLine("/// </remarks>"); base.WriteClassAttributes(writer, designer); } } }
注册CustomCodeGenerator 最后一步，在DbMigration配置文件中我们需要指定要使用的代码生成器，默认情况下在Migration文件夹中查找Configuration.cs ... internal sealed class Configuration : DbMigrationsConfiguration<YourApplication.Database.Context> { public Configuration() { // I recommend that auto-migrations be disabled so that we control // the migrations explicitly AutomaticMigrationsEnabled = false; CodeGenerator = new EFExtensions.CustomCodeGenerator(); } protected override void Seed(YourApplication.Database.Context context) { // Your custom seed logic here } }

Answer 8

从EF Core 2.1开始，您可以在更改列之前使用MigrationBuilder.UpdateData更改值（比使用原始SQL更干净）：

protected override void Up(MigrationBuilder migrationBuilder)
{
    // Change existing NULL values to NOT NULL values
    migrationBuilder.UpdateData(
        table: tableName,
        column: columnName,
        value: valueInsteadOfNull,
        keyColumn: columnName,
        keyValue: null);

    // Change column type to NOT NULL
    migrationBuilder.AlterColumn<ColumnType>(
        table: tableName,
        name: columnName,
        nullable: false,
        oldClrType: typeof(ColumnType),
        oldNullable: true);
}

Entity Framework迁移中必填字段的默认值？

问题描述投票：83回答：8

8个回答

最新问题

Entity Framework迁移中必填字段的默认值？

问题描述 投票：83回答：8

8个回答

最新问题

问题描述投票：83回答：8