修复达梦EFCore驱动布尔类型兼容问题

dm库相比其他库本身缺少一些语法差异，也可以说是缺陷。
比如：
0和1无法直接在sql中当作真假值用，where 0这种写法不支持，报错：查询使用值表达式作为过滤条件；
t.field is null 也无法直接作为select项；
不支持OUTER APPLY等SQL语法；
以及数据库函数中的又只能用0和1作为布尔参数值。

但是dm.efcore生成的语句就是这样的，现在来给修复办法。

1.查询使用值表达式作为过滤条件

这个问题其实不好修，正常的修复办法需要重写很多代码，主要是EFCore里面的这个代码SqlNullabilityProcessor，主要就是为了优化sql语句的

• a == true -> a

a == true -> a 变成where a这样，就是这个代码导致的，但是很遗憾达梦不支持。

public class SqlNullabilityProcessor
{.....private SqlExpression OptimizeComparison(SqlBinaryExpression sqlBinaryExpression,SqlExpression left,SqlExpression right,bool leftNullable,bool rightNullable,out bool nullable){var leftNullValue = leftNullable && left is SqlConstantExpression or SqlParameterExpression;var rightNullValue = rightNullable && right is SqlConstantExpression or SqlParameterExpression;// a == null -> a IS NULL// a != null -> a IS NOT NULLif (rightNullValue){var result = sqlBinaryExpression.OperatorType == ExpressionType.Equal? ProcessNullNotNull(_sqlExpressionFactory.IsNull(left), leftNullable): ProcessNullNotNull(_sqlExpressionFactory.IsNotNull(left), leftNullable);nullable = false;return result;}// null == a -> a IS NULL// null != a -> a IS NOT NULLif (leftNullValue){var result = sqlBinaryExpression.OperatorType == ExpressionType.Equal? ProcessNullNotNull(_sqlExpressionFactory.IsNull(right), rightNullable): ProcessNullNotNull(_sqlExpressionFactory.IsNotNull(right), rightNullable);nullable = false;return result;}if (TryGetBool(right, out var rightBoolValue)&& !leftNullable&& left.TypeMapping!.Converter == null){nullable = leftNullable;// only correct in 2-value logic// a == true -> a// a == false -> !a// a != true -> !a// a != false -> areturn sqlBinaryExpression.OperatorType == ExpressionType.Equal ^ rightBoolValue? OptimizeNonNullableNotExpression(_sqlExpressionFactory.Not(left)): left;}if (TryGetBool(left, out var leftBoolValue)&& !rightNullable&& right.TypeMapping!.Converter == null){nullable = rightNullable;// only correct in 2-value logic// true == a -> a// false == a -> !a// true != a -> !a// false != a -> areturn sqlBinaryExpression.OperatorType == ExpressionType.Equal ^ leftBoolValue? OptimizeNonNullableNotExpression(_sqlExpressionFactory.Not(right)): right;}// only correct in 2-value logic// a == a -> true// a != a -> falseif (!leftNullable&& left.Equals(right)){nullable = false;return _sqlExpressionFactory.Constant(sqlBinaryExpression.OperatorType == ExpressionType.Equal,sqlBinaryExpression.TypeMapping);}if (!leftNullable&& !rightNullable&& sqlBinaryExpression.OperatorType is ExpressionType.Equal or ExpressionType.NotEqual){var leftUnary = left as SqlUnaryExpression;var rightUnary = right as SqlUnaryExpression;var leftNegated = IsLogicalNot(leftUnary);var rightNegated = IsLogicalNot(rightUnary);if (leftNegated){left = leftUnary!.Operand;}if (rightNegated){right = rightUnary!.Operand;}// a == b <=> !a == !b -> a == b// !a == b <=> a == !b -> a != b// a != b <=> !a != !b -> a != b// !a != b <=> a != !b -> a == bnullable = false;return sqlBinaryExpression.OperatorType == ExpressionType.Equal ^ leftNegated == rightNegated? _sqlExpressionFactory.NotEqual(left, right): _sqlExpressionFactory.Equal(left, right);}nullable = false;return sqlBinaryExpression.Update(left, right);}
}

本来像的修复办法是重写这个类，但是这个方法不是虚方法还是私有的，无法重写，就需要从调用这个方法的所有方法全部重写，这就太麻烦了，这种重写还会有其他问题，比如下次升级efcore时，新版本的这个方法有改动，但我重写了就需要再重新重写一次。
在想不到办法的时候，无意间注意到这个方法转换0 和1 的地方就时TryGetBool这个几个if判断中（本来就时想改这里），都有下面这个判断
XXX.TypeMapping!.Converter == null
那么我就想如果boolTypeMapping.Converter不是null的不就可以绕过这个转换了吗。
所以就有了下面这个解决办法，直接上代码，不解释了，都能看懂：

public class MyDmBoolTypeMapping : BoolTypeMapping
{public MyDmBoolTypeMapping(string storeType, DbType? dbType): base(new RelationalTypeMappingParameters(new(typeof(bool), new DmBooleanConverter(), null), storeType)){}protected MyDmBoolTypeMapping(RelationalTypeMappingParameters parameters): base(parameters){}protected override string GenerateNonNullSqlLiteral(object value){if (!(bool)value){return "0";}return "1";}protected override RelationalTypeMapping Clone(RelationalTypeMappingParameters parameters){return (RelationalTypeMapping)(object)new MyDmBoolTypeMapping(parameters);}private sealed class DmBooleanConverter : ValueConverter<bool, bool>{public DmBooleanConverter(): base(b => b, b => b){}}
}
public class MyDmTypeMappingSource：DmTypeMappingSource
{public MyDmTypeMappingSource([NotNull] TypeMappingSourceDependencies dependencies, [NotNull] RelationalTypeMappingSourceDependencies relationalDependencies): base(dependencies, relationalDependencies){var f = typeof(DmTypeMappingSource).GetField("_bool",BindingFlags.Instance| BindingFlags.NonPublic);f.SetValue(this,new MyDmBoolTypeMapping("BIT", DbType.Boolean));}
}

上面代码就时给Bool类型的加上了Converter，它不再是null了，同样像上一个dmefcore驱动文章说的一样，用把这个MyDmTypeMappingSource替换服务类

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{base.OnConfiguring(optionsBuilder);optionsBuilder.ReplaceService<IRelationalTypeMappingSource, MyDmTypeMappingSource>();
}

到这里就解决了a == true -> a这一种“查询使用值表达式作为过滤条件”报错问题，但是不彻底，还会有其他比如 a.Contains(t.Id) -> false这样的情况，当然还有其他很多情况。
无法直接改代码修复，我又继续思考，然后我发现达梦不支持0和1作为条件，但是支持false和true这样的作为条件，那么我就把这个MyDmBoolTypeMapping中的GenerateNonNullSqlLiteral方法改成返回FALSE和TRUE不就可以了吗，所以就有了下面的代码，验证发现完美解决问题

public class MyDmBoolTypeMapping : BoolTypeMapping
{public MyDmBoolTypeMapping(string storeType, DbType? dbType): base(new RelationalTypeMappingParameters(new(typeof(bool), new DmBooleanConverter(), null), storeType)){}protected MyDmBoolTypeMapping(RelationalTypeMappingParameters parameters): base(parameters){}protected override string GenerateNonNullSqlLiteral(object value){if (!(bool)value){return "FALSE";}return "TRUE";}protected override RelationalTypeMapping Clone(RelationalTypeMappingParameters parameters){return (RelationalTypeMapping)(object)new MyDmBoolTypeMapping(parameters);}private sealed class DmBooleanConverter : ValueConverter<bool, bool>{public DmBooleanConverter(): base(b => b, b => b){}}
}

2.数据库函数中的又只能用0和1作为布尔参数值

先说函数这个问题，因为我们改成了FALSE和TRUE导致的，那么我再继续重写：

public class MyDmSqlNullabilityProcessor : SqlNullabilityProcessor
{protected override SqlExpression VisitSqlFunction(SqlFunctionExpression sqlFunctionExpression, bool allowOptimizedExpansion, out bool nullable){var exp = base.VisitSqlFunction(sqlFunctionExpression, allowOptimizedExpansion, out nullable);if (exp is SqlFunctionExpression functionExpression){var arguments = functionExpression.Arguments.Select(e =>{if (e is SqlConstantExpression constantExpression && constantExpression.Value is bool value){return _sqlExpressionFactory.Constant(value ? 1 : 0, new IntTypeMapping("INT", DbType.Int32));}return e;}).ToArray();return functionExpression.Update(functionExpression.Instance, arguments);}return exp;}
}

3.其他问题

主要修复代码就是下面这个，关键代码是这行UpdateShaperExpression(Visit(shapedQueryExpression.ShaperExpression))
同样需要其他类new它并且跟其他服务类一样替换注入，就不多解释了。

public class MySearchConditionConvertingExpressionVisitor : SearchConditionConvertingExpressionVisitor
{protected override Expression VisitExtension(Expression extensionExpression)=> extensionExpression switch{ShapedQueryExpression shapedQueryExpression=> shapedQueryExpression.UpdateQueryExpression(Visit(shapedQueryExpression.QueryExpression)).UpdateShaperExpression(Visit(shapedQueryExpression.ShaperExpression)),_ => base.VisitExtension(extensionExpression),};
}

完