IM_NEW/MessageService.Infrastructure/Migrations/20260911000100_ConversationUniqueness.cs

using Microsoft.EntityFrameworkCore.Infrastructure;
using Microsoft.EntityFrameworkCore.Migrations;

namespace MessageService.Infrastructure.Migrations
{
    [DbContext(typeof(MessageDbContext))]
    [Migration("20260911000100_ConversationUniqueness")]
    public partial class ConversationUniqueness : Migration
    {
        protected override void Up(MigrationBuilder migrationBuilder)
        {
            migrationBuilder.Sql("""
                CREATE TEMPORARY TABLE `conversation_dedup` AS
                SELECT
                    `Id`,
                    ROW_NUMBER() OVER (
                        PARTITION BY `UserId`, `ChatType`, `TargetId`
                        ORDER BY COALESCE(`ModificationTime`, `CreationTime`) DESC, `Id` DESC
                    ) AS `row_num`,
                    MAX(`UnreadCount`) OVER (
                        PARTITION BY `UserId`, `ChatType`, `TargetId`
                    ) AS `max_unread_count`,
                    MAX(`LastReadSequenceId`) OVER (
                        PARTITION BY `UserId`, `ChatType`, `TargetId`
                    ) AS `max_last_read_sequence_id`
                FROM `conversations`
                WHERE `IsDeleted` = 0;
                """);

            migrationBuilder.Sql("""
                UPDATE `conversations` AS `conversation`
                INNER JOIN `conversation_dedup` AS `dedup` ON `conversation`.`Id` = `dedup`.`Id`
                SET
                    `conversation`.`UnreadCount` = CASE
                        WHEN `dedup`.`row_num` = 1 THEN `dedup`.`max_unread_count`
                        ELSE `conversation`.`UnreadCount`
                    END,
                    `conversation`.`LastReadSequenceId` = CASE
                        WHEN `dedup`.`row_num` = 1 THEN `dedup`.`max_last_read_sequence_id`
                        ELSE `conversation`.`LastReadSequenceId`
                    END,
                    `conversation`.`IsDeleted` = CASE
                        WHEN `dedup`.`row_num` = 1 THEN `conversation`.`IsDeleted`
                        ELSE 1
                    END,
                    `conversation`.`Deletion` = CASE
                        WHEN `dedup`.`row_num` = 1 THEN `conversation`.`Deletion`
                        ELSE CURRENT_TIMESTAMP(6)
                    END;
                """);

            migrationBuilder.Sql("DROP TEMPORARY TABLE `conversation_dedup`;");

            migrationBuilder.AddColumn<string>(
                name: "ActiveConversationKey",
                table: "conversations",
                type: "varchar(96)",
                maxLength: 96,
                nullable: true,
                computedColumnSql: "CASE WHEN `IsDeleted` = 0 THEN CONCAT(`UserId`, ':', `ChatType`, ':', `TargetId`) ELSE NULL END",
                stored: true);

            migrationBuilder.CreateIndex(
                name: "UX_conversations_ActiveConversationKey",
                table: "conversations",
                column: "ActiveConversationKey",
                unique: true);
        }

        protected override void Down(MigrationBuilder migrationBuilder)
        {
            migrationBuilder.DropIndex(
                name: "UX_conversations_ActiveConversationKey",
                table: "conversations");

            migrationBuilder.DropColumn(
                name: "ActiveConversationKey",
                table: "conversations");
        }
    }
}