关于EFCore插件API使用中踩过的坑
本文基于efcore8.0，参考文档。假设需要重写efcore或者特定数据库的方法的SQL转换，按上面文档及其示例代码，本例中我们大概就是提供下面几个接口的实现。
[*]IMethodCallTranslator
[*]IMethodCallTranslatorPlugin
[*]IDbContextOptionsExtension
[*]以及特定数据库的DbContextOptionsBuilder（如SqlServerDbContextOptionsBuilder）扩展方法
后面再说说踩过的坑（总结）！
示例
public class MyMethodCallTranslator:IMethodCallTranslator
{
private readonly SqlServerSqlExpressionFactory _sqlExpressionFactory;
public MyMethodCallTranslator(SqlServerSqlExpressionFactory sqlExpressionFactory)
{
_sqlExpressionFactory=sqlExpressionFactory
}
public virtual SqlExpression Translate(SqlExpression instance, MethodInfo method, IReadOnlyList<SqlExpression> arguments,IDiagnosticsLogger<DbLoggerCategory.Query> logger)
{
//你需要的转换代码，并返回你的SqlExpression
return null;
}
}
public class MyMethodCallTranslatorPlugin:IMethodCallTranslatorPlugin
{
public IEnumerable<IMethodCallTranslator> Translators{get;}
//坑1：这里注入时不能用SqlServerSqlExpressionFactory，无法解析SqlServerSqlExpressionFactory，只能ISqlExpressionFactory注入后再强转成SqlServerSqlExpressionFactory
public MyMethodCallTranslatorPlugin(ISqlExpressionFactory sqlExpressionFactory)
{
Translators=new List<IMethodCallTranslator>()
{
new MyMethodCallTranslator((SqlServerSqlExpressionFactory)sqlExpressionFactory)
}
}
}
public class MyDbContextOptionsExtension:IDbContextOptionsExtension
{
private DbContextOptionsExtensionInfo? _info;
public virtual void ApplyServices(IServiceCollection services)
{
//坑2：必须用new EntityFrameworkRelationalServicesBuilder(services)再添加服务，不能直接用services添加
new EntityFrameworkRelationalServicesBuilder(services)
.TryAdd<IMethodCallTranslatorPlugin, MyMethodCallTranslatorPlugin>();
}
public virtual DbContextOptionsExtensionInfo Info
=> _info ??= new ExtensionInfo(this);
public virtual void Validate(IDbContextOptions options)
{
}
private sealed class ExtensionInfo(IDbContextOptionsExtension extension) : DbContextOptionsExtensionInfo(extension)
{
public override bool IsDatabaseProvider => false;
public override int GetServiceProviderHashCode() => 0;
public override bool ShouldUseSameServiceProvider(DbContextOptionsExtensionInfo other)
=> other is ExtensionInfo;
public override void PopulateDebugInfo(IDictionary<string, string> debugInfo)
{
}
public override string LogFragment => "";
}
}
public static class MySqlServerDbContextOptionsBuilder Extensions
{
//坑3：这里要用具体数据库的...DbContextOptionsBuilder，用DbContextOptionsBuilder也行，但是就无法注入具体的ISqlExpressionFactory
//关键是SqlServerDbContextOptionsBuilder不是从DbContextOptionsBuilder继承的，看名称似乎是继承的，其实不是
public static SqlServerDbContextOptionsBuilder Use...(this SqlServerDbContextOptionsBuilder optionsBuilder)
{
var coreOptionsBuilder = ((IRelationalDbContextOptionsBuilderInfrastructure)optionsBuilder).OptionsBuilder;
var extension = coreOptionsBuilder.Options.FindExtension<MyDbContextOptionsExtension>()
?? new MyDbContextOptionsExtension();
((IDbContextOptionsBuilderInfrastructure)coreOptionsBuilder).AddOrUpdateExtension(extension);
return optionsBuilder;
}
}总结
1. ISqlExpressionFactory
注入时不能用SqlServerSqlExpressionFactory，无法解析SqlServerSqlExpressionFactory，只能ISqlExpressionFactory注入后再强转成SqlServerSqlExpressionFactory
2. EntityFrameworkRelationalServicesBuilder
必须用new EntityFrameworkRelationalServicesBuilder(services)再添加服务，不能直接用services添加
3. DbContextOptionsBuilder
这里要用具体数据库的...DbContextOptionsBuilder，用DbContextOptionsBuilder也行，但是就无法注入具体的ISqlExpressionFactory
关键是SqlServerDbContextOptionsBuilder不是从DbContextOptionsBuilder继承的，看名称似乎是继承的，其实不是
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