Entity framework 核心迁移：将列从不可空更改为可空，然后将值设置为空

Question

我决定将一列从不可空列更改为可空列。这里没问题。我将属性改为“?”在类型中 (DateTime => DateTime?) 并且生成的迁移正常。

不过，我想将被视为“null”的值更改为真正的 null。意思是，将值 0001-01-01 00:00:00 更改为 null.

我创建了一个扩展方法，可以正确生成 SQL 向上和向下代码。我在 Up 中的列更改之后和 Down 中之前执行了此操作。

执行 Up 时出现问题，因为我的扩展方法中的 SQL 在应用列更改的更改之前执行。

有没有办法在执行这条语句之前强制应用更改？（请参阅可以插入代码的代码中的 FIXME。可能有两个位置。）

扩展名class

public static class MigrationsCorrections
{
    public static OperationBuilder<SqlOperation> ChangeDateToNullable(this MigrationBuilder migrationBuilder, string table, string column)
    {
        //FIXME: Either having a call here this to force previous changes to be applied
        return migrationBuilder.Sql($"UPDATE {table} SET {column} = null WHERE {column} = '0001-01-01 00:00:00';");
    }

    public static OperationBuilder<SqlOperation> ChangeDateToNotNullable(this MigrationBuilder migrationBuilder, string table, string column)
    {
        return migrationBuilder.Sql($"UPDATE {table} SET {column} = '0001-01-01 00:00:00' WHERE {column} = null;");
    }
}

迁移class

// IMPORTATION OF THE EXTENSION CLASS
public partial class MetaPersonBirthDateNullable : Migration
{
    protected override void Up(MigrationBuilder migrationBuilder)
    {
        migrationBuilder.AlterColumn<DateTime>(
            name: "BirthDay",
            table: "MetaPersons",
            type: "TEXT",
            nullable: true,
            oldClrType: typeof(DateTime),
            oldType: "TEXT");
        //FIXME: Either having a call here this to force previous changes to be applied
        migrationBuilder.ChangeDateToNullable("MetaPersons", "BirthDay");
    }

    protected override void Down(MigrationBuilder migrationBuilder)
    {
        migrationBuilder.ChangeDateToNotNullable("MetaPersons", "BirthDay");
        migrationBuilder.AlterColumn<DateTime>(
            name: "BirthDay",
            table: "MetaPersons",
            type: "TEXT",
            nullable: false,
            defaultValue: new DateTime(1, 1, 1, 0, 0, 0, 0, DateTimeKind.Unspecified),
            oldClrType: typeof(DateTime),
            oldType: "TEXT",
            oldNullable: true);
    }
}

SQL 迁移生成

BEGIN TRANSACTION;

UPDATE MetaPersons SET BirthDay = null WHERE BirthDay = '0001-01-01 00:00:00';

CREATE TABLE "ef_temp_MetaPersons" (
    "Id" INTEGER NOT NULL CONSTRAINT "PK_MetaPersons" PRIMARY KEY AUTOINCREMENT,
    "BirthDay" TEXT NULL,
    "DeathDay" TEXT NULL,
    "ExternalId" TEXT NULL,
    "MetaSource" TEXT NULL,
    "Name" TEXT COLLATE NOCASE NULL,
    "Professions" TEXT NULL
);

INSERT INTO "ef_temp_MetaPersons" ("Id", "BirthDay", "DeathDay", "ExternalId", "MetaSource", "Name", "Professions")
SELECT "Id", "BirthDay", "DeathDay", "ExternalId", "MetaSource", "Name", "Professions"
FROM "MetaPersons";

COMMIT;

PRAGMA foreign_keys = 0;

BEGIN TRANSACTION;

DROP TABLE "MetaPersons";

ALTER TABLE "ef_temp_MetaPersons" RENAME TO "MetaPersons";

COMMIT;

PRAGMA foreign_keys = 1;

BEGIN TRANSACTION;

CREATE UNIQUE INDEX "IX_MetaPersons_ExternalId_MetaSource" ON "MetaPersons" ("ExternalId", "MetaSource");

CREATE INDEX "IX_MetaPersons_Name" ON "MetaPersons" ("Name");

INSERT INTO "__EFMigrationsHistory" ("MigrationId", "ProductVersion")
VALUES ('20220309145323_MetaPerson.BirthDate Nullable', '6.0.2');

COMMIT;

正如我们所见，UPDATE语句的顺序不正确

编辑 1

我尝试使用 MigrationOperation class 代替 Microsoft Custom Migration，但我得到...

'ChangeDateToNullable' 类型的操作将在待重建 table 'MetaPersons' 时尝试。数据库可能未处于预期状态。查看此迁移生成的 SQL 以帮助诊断任何故障。考虑将这些操作移至后续迁移。

这个特殊的解决方案是我认为的，进行第二次迁移，但这不是我想要的，因为这些更改是联系在一起的。

Answer 1

来自文档 Using MigrationBuilder.Sql():

Use the EXEC function when a statement must be the first or only one in a SQL batch. It might also be needed to work around parser errors in idempotent migration scripts that can occur when referenced columns don't currently exist on a table.

所以最好创建两个迁移，一个用于 ALTER，另一个用于 UPDATE。

Answer 2

我解决了 MigrationOperations 方向的问题。我覆盖了 IMigrationsSqlGenerator.

的生成方法

为了有一个通用的解决方案，我创建了一个新的 Database 项目，其中包括这个新的 MigrationsSqlGenerator 和类需要改变日期列值 from/to 为空。我还添加了两个类来执行任何遵守顺序的 SQL 代码，从而允许在更改列后更改列的值。而这一切，都在同一次迁移中。

请参阅 https://github.com/djon2003/com.cyberinternauts.csharp.Database 了解完整的解决方案。

和 https://www.codeproject.com/Articles/5327089/Executing-SQL-code-within-EntityFrameworkCore-migr 相关文章。

生成的最终 SQL 代码：

BEGIN TRANSACTION;

CREATE TABLE "ef_temp_MetaPersons" (
    "Id" INTEGER NOT NULL CONSTRAINT "PK_MetaPersons" PRIMARY KEY AUTOINCREMENT,
    "BirthDay" TEXT NULL,
    "DeathDay" TEXT NULL,
    "ExternalId" TEXT NULL,
    "MetaSource" TEXT NULL,
    "Name" TEXT COLLATE NOCASE NULL,
    "Professions" TEXT NULL
);

INSERT INTO "ef_temp_MetaPersons" ("Id", "BirthDay", "DeathDay", "ExternalId", "MetaSource", "Name", "Professions")
SELECT "Id", "BirthDay", "DeathDay", "ExternalId", "MetaSource", "Name", "Professions"
FROM "MetaPersons";

COMMIT;

PRAGMA foreign_keys = 0;

BEGIN TRANSACTION;

DROP TABLE "MetaPersons";

ALTER TABLE "ef_temp_MetaPersons" RENAME TO "MetaPersons";

COMMIT;

PRAGMA foreign_keys = 1;

BEGIN TRANSACTION;

CREATE UNIQUE INDEX "IX_MetaPersons_ExternalId_MetaSource" ON "MetaPersons" ("ExternalId", "MetaSource");

CREATE INDEX "IX_MetaPersons_Name" ON "MetaPersons" ("Name");

UPDATE "MetaPersons" SET "BirthDay" = null WHERE "BirthDay" = '0001-01-01 00:00:00';

INSERT INTO "__EFMigrationsHistory" ("MigrationId", "ProductVersion")
VALUES ('20220309145323_MetaPerson.BirthDate Nullable', '6.0.2');

COMMIT;

可以看到，现在UPDATE语句在列修改之后

Entity framework 核心迁移：将列从不可空更改为可空，然后将值设置为空

Entity framework core migration: Change column from non-nullable to nullable then set values to null

c#

sqlite

entity-framework-core