.net core 2 中多个表的 IDENTITY_INSERT

Question

我正在尝试将数据从现有数据库迁移到新数据库。旧数据库非常复杂，这意味着大多数表都基于外部 id 与许多其他表有关系。我遇到了这个插入 id 的解决方案：

using (var context = new EmployeeContext())
{
    context.Employees.Add(new Employee { EmployeeId = 100, Name = "John Doe" });
    context.Employees.Add(new Employee { EmployeeId = 101, Name = "Jane Doe" });

    context.Database.OpenConnection();
    try
    {
        context.Database.ExecuteSqlCommand("SET IDENTITY_INSERT dbo.Employees ON");
        context.SaveChanges();
        context.Database.ExecuteSqlCommand("SET IDENTITY_INSERT dbo.Employees OFF");
    }
    finally
    {
        context.Database.CloseConnection();
    }


    foreach (var employee in context.Employees)
    {
        Console.WriteLine(employee.EmployeeId + ": " + employee.Name);
    }
}

来自此 Microsoft 指南：https://docs.microsoft.com/en-us/ef/core/saving/explicit-values-generated-properties

有没有办法在应用context.SaveChanges();之前在多个表上设置IDENTITY_INSERT？

Answer 1

不。查看 IDENTITY_INSERT 的文档。 https://docs.microsoft.com/en-us/sql/t-sql/statements/set-identity-insert-transact-sql

它明确指出：

在任何时候，一个会话中只有一个表可以有 IDENTITY_INSERT 属性设置为 ON。如果表已经将此属性设置为 ON， 并为另一个表发出 SET IDENTITY_INSERT ON 语句， SQL Server 返回一条错误消息，指出 SET IDENTITY_INSERT 是 已经开启并报告它设置为开启的表。

Answer 2

我在从存储在 json 文件中的对象树中播种数据时遇到了同样的问题。

例子：

jsonData = System.IO.File.ReadAllText(@"Data\InputParameters.json");
var inputParameters = JsonConvert.DeserializeObject<List<ParameterCategory>> jsonData, settings);
context.AddRange(inputParameters);
context.SaveChanges();

查看 EFCore 源代码后，我想出了以下解决方案：

1.新建一个类“SqlServerUpdateSqlGeneratorInsertIdentity”，负责为每个插入操作开启和关闭Identity_Insert：

using System.Collections.Generic;
using System.Linq;
using System.Text;

using Microsoft.EntityFrameworkCore.SqlServer.Update.Internal;
using Microsoft.EntityFrameworkCore.Storage;
using Microsoft.EntityFrameworkCore.Update;

/// <summary>
/// SqlServerUpdateSqlGenerator with Insert_Identity.
/// </summary>
public class SqlServerUpdateSqlGeneratorInsertIdentity : SqlServerUpdateSqlGenerator
{
    /// <summary>
    /// Initializes a new instance of the <see cref="SqlServerUpdateSqlGeneratorInsertIdentity"/> class.
    /// </summary>
    /// <param name="dependencies">The dependencies.</param>
    public SqlServerUpdateSqlGeneratorInsertIdentity(UpdateSqlGeneratorDependencies dependencies)
        : base(dependencies)
    {
    }

    /// <inheritdoc/>
    public override ResultSetMapping AppendBulkInsertOperation(
        StringBuilder commandStringBuilder,
        IReadOnlyList<ModificationCommand> modificationCommands,
        int commandPosition)
    {
        var columns = modificationCommands[0].ColumnModifications.Where(o => o.IsWrite).Select(o => o.ColumnName)
            .ToList();
        var schema = modificationCommands[0].Schema;
        var table = modificationCommands[0].TableName;

        GenerateIdentityInsert(commandStringBuilder, table, schema, columns, on: true);
        var result = base.AppendBulkInsertOperation(commandStringBuilder, modificationCommands, commandPosition);
        GenerateIdentityInsert(commandStringBuilder, table, schema, columns, on: false);

        return result;
    }

    private void GenerateIdentityInsert(
        StringBuilder builder,
        string table,
        string schema,
        IEnumerable<string> columns,
        bool on)
    {
        var stringTypeMapping = Dependencies.TypeMappingSource.GetMapping(typeof(string));

        builder.Append("IF EXISTS (SELECT * FROM [sys].[identity_columns] WHERE").Append(" [name] IN (")
            .Append(string.Join(", ", columns.Select(stringTypeMapping.GenerateSqlLiteral)))
            .Append(") AND [object_id] = OBJECT_ID(").Append(
                stringTypeMapping.GenerateSqlLiteral(
                    Dependencies.SqlGenerationHelper.DelimitIdentifier(table, schema))).AppendLine("))");

        builder.Append("SET IDENTITY_INSERT ")
            .Append(Dependencies.SqlGenerationHelper.DelimitIdentifier(table, schema)).Append(on ? " ON" : " OFF")
            .AppendLine(Dependencies.SqlGenerationHelper.StatementTerminator);
    }
}

2.将原来的“SqlServerUpdateSqlGenerator”替换为继承的新的：

在 Startup.cs - ConfigureServices 中使用以下代码：

services.AddDbContext<YourDataContext>(options =>
{
    options.UseSqlServer(YourConnectionString);
    options.ReplaceService<ISqlServerUpdateSqlGenerator, SqlServerUpdateSqlGeneratorInsertIdentity>();
});

或在 YourDataContext.cs - OnConfiguring 使用这个（未测试）：

options.ReplaceService<ISqlServerUpdateSqlGenerator, SqlServerUpdateSqlGeneratorInsertIdentity>();

在播种后可能需要将服务配置重置为原始配置。在我的情况下，它不是。

希望对某人有所帮助...