以上答案确实有帮助，但仅提供了部分解决方案。主要问题是，一旦删除“默认值”属性，就不会删除对数据库中列的约束。因此，以前的默认值仍将保留在数据库中。
这是该问题的完整解决方案，包括删除属性删除方面的SQL约束。我还重用了.NET Framework的本机DefaultValue属性。
用法
[DatabaseGenerated(DatabaseGeneratedOption.Computed)]
[DefaultValue("getutcdate()")]
public DateTime CreatedOn { get; set; }
为此，您需要更新IdentityModels.cs和Configuration.cs文件
IdentityModels.cs文件
在您的ApplicationDbContext班级中添加/更新此方法
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
var convention = new AttributeToColumnAnnotationConvention<DefaultValueAttribute, string>("SqlDefaultValue", (p, attributes) => attributes.SingleOrDefault().Value.ToString());
modelBuilder.Conventions.Add(convention);
}
Configuration.cs文件
Configuration通过注册自定义Sql生成器来更新类构造函数，如下所示：
internal sealed class Configuration : DbMigrationsConfiguration<ApplicationDbContext>
{
public Configuration()
{
// DefaultValue Sql Generator
SetSqlGenerator("System.Data.SqlClient", new DefaultValueSqlServerMigrationSqlGenerator());
}
}
接下来，添加自定义Sql生成器类（可以将其添加到Configuration.cs文件或单独的文件中）
internal class DefaultValueSqlServerMigrationSqlGenerator : SqlServerMigrationSqlGenerator
{
private int dropConstraintCount = 0;
protected override void Generate(AddColumnOperation addColumnOperation)
{
SetAnnotatedColumn(addColumnOperation.Column, addColumnOperation.Table);
base.Generate(addColumnOperation);
}
protected override void Generate(AlterColumnOperation alterColumnOperation)
{
SetAnnotatedColumn(alterColumnOperation.Column, alterColumnOperation.Table);
base.Generate(alterColumnOperation);
}
protected override void Generate(CreateTableOperation createTableOperation)
{
SetAnnotatedColumns(createTableOperation.Columns, createTableOperation.Name);
base.Generate(createTableOperation);
}
protected override void Generate(AlterTableOperation alterTableOperation)
{
SetAnnotatedColumns(alterTableOperation.Columns, alterTableOperation.Name);
base.Generate(alterTableOperation);
}
private void SetAnnotatedColumn(ColumnModel column, string tableName)
{
AnnotationValues values;
if (column.Annotations.TryGetValue("SqlDefaultValue", out values))
{
if (values.NewValue == null)
{
column.DefaultValueSql = null;
using (var writer = Writer())
{
// Drop Constraint
writer.WriteLine(GetSqlDropConstraintQuery(tableName, column.Name));
Statement(writer);
}
}
else
{
column.DefaultValueSql = (string)values.NewValue;
}
}
}
private void SetAnnotatedColumns(IEnumerable<ColumnModel> columns, string tableName)
{
foreach (var column in columns)
{
SetAnnotatedColumn(column, tableName);
}
}
private string GetSqlDropConstraintQuery(string tableName, string columnName)
{
var tableNameSplittedByDot = tableName.Split('.');
var tableSchema = tableNameSplittedByDot[0];
var tablePureName = tableNameSplittedByDot[1];
var str = $@"DECLARE @var{dropConstraintCount} nvarchar(128)
SELECT @var{dropConstraintCount} = name
FROM sys.default_constraints
WHERE parent_object_id = object_id(N'{tableSchema}.[{tablePureName}]')
AND col_name(parent_object_id, parent_column_id) = '{columnName}';
IF @var{dropConstraintCount} IS NOT NULL
EXECUTE('ALTER TABLE {tableSchema}.[{tablePureName}] DROP CONSTRAINT [' + @var{dropConstraintCount} + ']')";
dropConstraintCount = dropConstraintCount + 1;
return str;
}
}
this.Active = true;？我认为DB值在获取时将优先，但是要小心，如果new'ing然后附加一个实体进行更新而不先获取，因为更改跟踪可能会在您希望更新值时看到它。发表评论，因为我已经很长时间没有使用EF了，我觉得这是在黑暗中拍摄。