在Linux平台下使用.NET Core访问Access数据库读取mdb文件数据

今天有群友在群里问 C# 能不能在 Linux 下访问 Access数据库？

我觉得这很有趣，因此研究折腾了一下，也因为很久没有写博文了，所以特意上来写博文分享经验。

运行环境

• 操作系统：Ubuntu 22.04.3 LTS (Jammy)
• 开发工具：Visual Studio 2022 (17.8.0)
• 运行时版本：.NET Runtime 8.0
• 依赖库：unixodbc、mdbtools、odbc-mdbtools

依赖库安装

apt-get update
sudo apt-get install unixodbc mdbtools odbc-mdbtools

依赖库版本信息

• apt list --installed | grep odbc

libodbc1/jammy,now 2.3.9-5 amd64 [installed,automatic]
libodbc2/jammy,now 2.3.9-5 amd64 [installed,automatic]
libodbccr2/jammy,now 2.3.9-5 amd64 [installed,automatic]
libodbcinst2/jammy,now 2.3.9-5 amd64 [installed,automatic]
odbc-mdbtools/jammy,now 1.0.0+dfsg-1 amd64 [installed]
odbcinst1debian2/jammy,now 2.3.9-5 amd64 [installed,automatic]
odbcinst/jammy,now 2.3.9-5 amd64 [installed,automatic]
unixodbc-common/jammy,now 2.3.9-5 all [installed,automatic]
unixodbc/jammy,now 2.3.9-5 amd64 [installed]

• apt list --installed | grep mdb

liblmdb0/jammy,now 0.9.24-1build2 amd64 [installed,automatic]
libmdb3/jammy,now 1.0.0+dfsg-1 amd64 [installed,automatic]
libmdbsql3/jammy,now 1.0.0+dfsg-1 amd64 [installed,automatic]
mdbtools/jammy,now 1.0.0+dfsg-1 amd64 [installed]
odbc-mdbtools/jammy,now 1.0.0+dfsg-1 amd64 [installed]

Linux平台 下的 ODBC 配置

• /etc/odbc.ini

[access_db] # 随意命名，会在项目代码里用到它
Description=Microsoft Access Database
Driver=MDBW
ServerName = localhost
Database=/root/Database1.mdb # 按你的实际路径改写，要有读写权限

• /etc/odbcinst.ini

[MDBW] # 随意，在odbc.ini文件用到它
Description=MDBTools Driver Wide # 随意
Driver=/usr/lib/x86_64-linux-gnu/odbc/libmdbodbcW.so # 按你的实际路径改写
Setup=/usr/lib/x86_64-linux-gnu/odbc/libmdbodbcW.so # 按你的实际路径改写
FileUsage=1
UsageCount=1
[MDBTools]
Description=MDBTools Driver # 随意
Driver=/usr/lib/x86_64-linux-gnu/odbc/libmdbodbc.so # 按你的实际路径改写
Setup=/usr/lib/x86_64-linux-gnu/odbc/libmdbodbc.so # 按你的实际路径改写
FileUsage=1
UsageCount=1
[ODBC]
Trace=1
TraceFile=/tmp/mdb.log # 有写入权限的文件路径

Demo 项目代码

• OdbcForLinuxTestApp.csproj

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
    <RuntimeIdentifiers>linux-x64;win-x64</RuntimeIdentifiers>
    <SelfContained>true</SelfContained>
    <ProduceReferenceAssembly>false</ProduceReferenceAssembly>
    <AppendRuntimeIdentifierToOutputPath>false</AppendRuntimeIdentifierToOutputPath>
    <AppendTargetFrameworkToOutputPath>false</AppendTargetFrameworkToOutputPath>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="System.Data.Odbc" Version="8.0.0" />
    <PackageReference Include="System.Data.OleDb" Version="8.0.0" />
  </ItemGroup>
</Project>

• Program.cs

using System.Data;
using System.Data.Common;
using System.Data.Odbc;
using System.Data.OleDb;

namespace OdbcForLinuxTestApp;

internal sealed class Program
{
    static async Task Main(string[] args)
    {
        string connectionStrings;
        if (OperatingSystem.IsWindows())
        {
            string mdbFile = Path.Combine(AppContext.BaseDirectory, "Database1.mdb");
            connectionStrings = $"Provider=Microsoft.ACE.OLEDB.12.0;Data Source={mdbFile}";
        }
        else
        {
            //root/Database1.mdb
            connectionStrings = "DSN=access_db;";
        }

        await using (DbConnection conn = GetDbConnection(connectionStrings))
        {
            await conn.OpenAsync();
            DbCommand cmd = conn.CreateCommand();
            cmd.CommandType = CommandType.Text;
            cmd.CommandText = "select [ID],[UserName] from Users";

            DbDataReader reader = await cmd.ExecuteReaderAsync();
            while (await reader.ReadAsync())
            {
                //The MDBTools does not support the use of column names
                string userName = reader.GetString(1);
                Console.WriteLine("UserName: " + userName);
            }
        }
    }

    private static string DbProviderName => OperatingSystem.IsWindows() ? "System.Data.OleDb" : "System.Data.Odbc";

    private static DbConnection GetDbConnection(string connectionStrings)
    {
        RegisterOdbcOrOleDbFactory();
        DbProviderFactory dbFactory = DbProviderFactories.GetFactory(DbProviderName);
        DbConnection? conn = dbFactory.CreateConnection();
        if (conn == null)
        {
            return OperatingSystem.IsWindows() ? new OleDbConnection(connectionStrings) : new OdbcConnection(connectionStrings);
        }

        conn.ConnectionString = connectionStrings;
        return conn;
    }

    private static int _isRegisteredDbFactory;
    private static void RegisterOdbcOrOleDbFactory()
    {
        if (Interlocked.CompareExchange(ref _isRegisteredDbFactory, 1, 0) == 0)
        {
            string dbProviderName = DbProviderName;
            IEnumerable<string> providerInvariantNames = DbProviderFactories.GetProviderInvariantNames();
            string? invariantName = providerInvariantNames.FirstOrDefault(x => x.Equals(dbProviderName, StringComparison.InvariantCultureIgnoreCase));
            if (string.IsNullOrWhiteSpace(invariantName))
            {
                DbProviderFactories.RegisterFactory(dbProviderName, OdbcFactory.Instance);
            }
        }
    }
}

编译和发布 Demo 项目代码

准备工作

• 创建 OdbcForLinuxTestApp 目录
• 将上述两个代码文件放入 OdbcForLinuxTestApp 目录
• 安装 .NET SDK 8.0.100

编译和发布

在 OdbcForLinuxTestApp 目录下，执行命令：

dotnet publish -c Release -f net8.0 -r win-x64 -o ./publish/win-x64 # 如果只考虑 Linux平台，该命令可忽略
dotnet publish -c Release -f net8.0 -r linux-x64 -o ./publish/linux-x64

运行 OdbcForLinuxTestApp

注意：Database1.mdb 数据库文件需要提前放到正确的路径，以 odbc.ini文件 的 Database 配置项为准。

cd ./publish/linux-x64
chmod +x OdbcForLinuxTestApp # 授予可执行权限
./OdbcForLinuxTestApp

输出：

UserName: Allen
UserName: Joy

折腾过程中遇到的问题

1. 搜了几个配置例子，有的说 libmdbodbc.so 在 /usr/lib 目录下，
   也有的在 /usr/local/lib/odbc 目录下，而我最终是在 /usr/lib/x86_64-linux-gnu/odbc 目录下找到。

2. mdbtools 不支持使用列名访问，只能用列索引。

其它

• 参考：https://github.com/mdbtools/mdbtools/issues/347
• MDB Tools：https://mdbtools.github.io