How to add description to columns in Entity Framework

http://stackoverflow.com/questions/10080601/how-to-add-description-to-columns-in-entity-framework-4-3-code-first-using-migra

国外大牛的方案：

 public class DbDescriptionUpdater<TContext>
        where TContext : System.Data.Entity.DbContext
    {
        public DbDescriptionUpdater(TContext context)
        {
            this.context = context;
        }

        Type contextType;
        TContext context;
        DbTransaction transaction;
        public void UpdateDatabaseDescriptions()
        {
            contextType = typeof(TContext);
            this.context = context;
            var props = contextType.GetProperties(System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.Public);
            transaction = null;
            try
            {
                context.Database.Connection.Open();
                transaction = context.Database.Connection.BeginTransaction();
                foreach (var prop in props)
                {
                    if (prop.PropertyType.InheritsOrImplements((typeof(DbSet<>))))
                    {
                        var tableType = prop.PropertyType.GetGenericArguments()[0];
                        SetTableDescriptions(tableType);
                    }
                }
                transaction.Commit();
            }
            catch
            {
                if (transaction != null)
                    transaction.Rollback();
                throw;
            }
            finally
            {
                if (context.Database.Connection.State == System.Data.ConnectionState.Open)
                    context.Database.Connection.Close();
            }
        }

        private void SetTableDescriptions(Type tableType)
        {
            string fullTableName = context.GetTableName(tableType);
            Regex regex = new Regex(@"(\[\w+\]\.)?\[(?<table>.*)\]");
            Match match = regex.Match(fullTableName);
            string tableName;
            if (match.Success)
                tableName = match.Groups["table"].Value;
            else
                tableName = fullTableName;

            var tableAttrs = tableType.GetCustomAttributes(typeof(TableAttribute), false);
            if (tableAttrs.Length > 0)
                tableName = ((TableAttribute)tableAttrs[0]).Name;
            foreach (var prop in tableType.GetProperties(System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.Instance))
            {
                if (prop.PropertyType.IsClass && prop.PropertyType != typeof(string))
                    continue;
                var attrs = prop.GetCustomAttributes(typeof(DisplayAttribute), false);
                if (attrs.Length > 0)
                    SetColumnDescription(tableName, prop.Name, ((DisplayAttribute)attrs[0]).Name);
            }
        }

        private void SetColumnDescription(string tableName, string columnName, string description)
        {
            string strGetDesc = "select [value] from fn_listextendedproperty('MS_Description','schema','dbo','table',N'" + tableName + "','column',null) where objname = N'" + columnName + "';";
            var prevDesc = RunSqlScalar(strGetDesc);
            if (prevDesc == null)
            {
                RunSql(@"EXEC sp_addextendedproperty 
@name = N'MS_Description', @value = @desc,
@level0type = N'Schema', @level0name = 'dbo',
@level1type = N'Table',  @level1name = @table,
@level2type = N'Column', @level2name = @column;",
                                                       new SqlParameter("@table", tableName),
                                                       new SqlParameter("@column", columnName),
                                                       new SqlParameter("@desc", description));
            }
            else
            {
                RunSql(@"EXEC sp_updateextendedproperty 
@name = N'MS_Description', @value = @desc,
@level0type = N'Schema', @level0name = 'dbo',
@level1type = N'Table',  @level1name = @table,
@level2type = N'Column', @level2name = @column;",
                                                       new SqlParameter("@table", tableName),
                                                       new SqlParameter("@column", columnName),
                                                       new SqlParameter("@desc", description));
            }
        }

        DbCommand CreateCommand(string cmdText, params SqlParameter[] parameters)
        {
            var cmd = context.Database.Connection.CreateCommand();
            cmd.CommandText = cmdText;
            cmd.Transaction = transaction;
            foreach (var p in parameters)
                cmd.Parameters.Add(p);
            return cmd;
        }
        void RunSql(string cmdText, params SqlParameter[] parameters)
        {
            var cmd = CreateCommand(cmdText, parameters);
            cmd.ExecuteNonQuery();
        }
        object RunSqlScalar(string cmdText, params SqlParameter[] parameters)
        {
            var cmd = CreateCommand(cmdText, parameters);
            return cmd.ExecuteScalar();
        }

    }
    public static class ReflectionUtil
    {

        public static bool InheritsOrImplements(this Type child, Type parent)
        {
            parent = ResolveGenericTypeDefinition(parent);

            var currentChild = child.IsGenericType
                                   ? child.GetGenericTypeDefinition()
                                   : child;

            while (currentChild != typeof(object))
            {
                if (parent == currentChild || HasAnyInterfaces(parent, currentChild))
                    return true;

                currentChild = currentChild.BaseType != null
                               && currentChild.BaseType.IsGenericType
                                   ? currentChild.BaseType.GetGenericTypeDefinition()
                                   : currentChild.BaseType;

                if (currentChild == null)
                    return false;
            }
            return false;
        }

        private static bool HasAnyInterfaces(Type parent, Type child)
        {
            return child.GetInterfaces()
                .Any(childInterface =>
                {
                    var currentInterface = childInterface.IsGenericType
                        ? childInterface.GetGenericTypeDefinition()
                        : childInterface;

                    return currentInterface == parent;
                });
        }

        private static Type ResolveGenericTypeDefinition(Type parent)
        {
            var shouldUseGenericType = true;
            if (parent.IsGenericType && parent.GetGenericTypeDefinition() != parent)
                shouldUseGenericType = false;

            if (parent.IsGenericType && shouldUseGenericType)
                parent = parent.GetGenericTypeDefinition();
            return parent;
        }
    }

    public static class ContextExtensions
    {
        public static string GetTableName(this DbContext context, Type tableType)
        {
            MethodInfo method = typeof(ContextExtensions).GetMethod("GetTableName", new Type[] { typeof(DbContext) })
                             .MakeGenericMethod(new Type[] { tableType });
            return (string)method.Invoke(context, new object[] { context });
        }
        public static string GetTableName<T>(this DbContext context) where T : class
        {
            ObjectContext objectContext = ((IObjectContextAdapter)context).ObjectContext;

            return objectContext.GetTableName<T>();
        }

        public static string GetTableName<T>(this ObjectContext context) where T : class
        {
            string sql = context.CreateObjectSet<T>().ToTraceString();
            Regex regex = new Regex("FROM (?<table>.*) AS");
            Match match = regex.Match(sql);

            string table = match.Groups["table"].Value;
            return table;
        }
    }

调用方法：

In your Migrations/Configuration.cs file, add this at the end of the Seed method:

DbDescriptionUpdater<ContextClass> updater = new DbDescriptionUpdater<ContextClass>(context);
updater.UpdateDatabaseDescriptions();

Then in Package Manager Console type update-database and hit Enter. That's it.

The code uses [Display(Name="Description here")] attribute on your entity class properties to set the description.

Please report any bug or suggest improvements.