Question

我正在尝试将数据从现有数据库迁移到新数据库。旧数据库非常纠结，这意味着大多数表与基于外部ID的许多其他表有关系。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

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

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：

任何时候，会话中只有一个表可以拥有IDENTITY_INSERT 属性设置为ON。如果表已将此属性设置为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为已经打开并报告为其设置为ON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。

示例：

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

在查看了EFCore的源代码之后，我想到了以下解决方案：

1。。创建一个新类“ SqlServerUpdateSqlGeneratorInsertIdentity”，该类负责为每个插入操作打开和关闭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“ SqlServerUpdateSqlGenerator”：

在Startup.cs中-ConfigureServices使用以下代码：

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

Or （在YourDataContext.cs中）-OnConfiguring使用此选项（未经测试）：

options.ReplaceService<ISqlServerUpdateSqlGenerator, SqlServerUpdateSqlGeneratorInsertIdentity>();

播种后，可能有必要将服务配置重置为原始配置。就我而言，不是。

希望能帮助到某人...

.net core 2

2 个答案: