问题描述
我的目标是为 IMutableEntityType
设置过滤器,我在其中按 CurrentTenantId
列值选择数据行。
有关更多上下文,请参阅:https://github.com/dotnet/efcore/issues/23718
这已经由我完成了:
var parameter = Expression.Parameter(entityType.ClrType,"p");
// Todo: This filter is working,but we must prevent filtering with TenantId = 0
var workingFilter = Expression.Lambda(
Expression.Equal(
Expression.Property(parameter,colName),// See https://github.com/dotnet/efcore/issues/23718
Expression.MakeMemberAccess(Expression.Constant(myContext),currentTenantIdMemberInfo)
),parameter);
entityType.SetQueryFilter(filter);
但我想获取所有实体如果 TenantId == 0
,所以我写了这个 Lambda:
var conditionalExpression = Expression.IfThenElse(
// Check if TenantId > 0
Expression.GreaterThan(
Expression.MakeMemberAccess(Expression.Constant(myContext),currentTenantIdMemberInfo),Expression.Constant((long) 0)
),// build filter: (p) => p.{colName} == {myContext.CurrentTenantId}
// i.e. (p) => p.TenantId == 123)
Expression.Lambda(
Expression.Equal(
Expression.Property(parameter,// See https://github.com/dotnet/efcore/issues/23718
Expression.MakeMemberAccess(Expression.Constant(myContext),currentTenantIdMemberInfo)
)//,),// TenantId <= 0,so act like (p => p)
Expression.Lambda(Expression.Constant(parameter)) // just p // Todo: Not working
//Expression.Lambda(Expression.Constant(parameter),parameter) // p => p // Todo: Also not working...
);
var filter = Expression.Lambda(conditionalExpression);
但是在调用 entityType.SetQueryFilter(filter);
之后我有 InvalidOperationException
:
'The filter expression '() => IIF((value(My.Project.MyContext).CurrentTenantId > 0),() => (p.TenantId == value(My.Project.MyContext).CurrentTenantId),() => p)' specified for entity type 'MyEntity' is invalid. The expression must accept a single parameter of type 'My.Project.MyEntity' and return bool.'
我的问题是 - 我如何才能实现我的目标?
解决方法
类似的东西。您错过了向 Lambda 添加 parameter
并且在 lambda 使用中犯了错误。还选择了最短的方法来做到这一点。
var parameter = Expression.Parameter(entityType.ClrType,"p");
// EF just needs to know that you have member access to DbContext
var contextExpr = Expression.Constant(null,typeof(MyContext));
var tenantExpr = Expression.MakeMemberAccess(contextExpr,currentTenantIdMemberInfo);
var conditionalExpression = Expression.OrElse(
// Check if TenantId <= 0
Expression.LessThanOrEqual(
tenantExpr,Expression.Constant((long) 0)
),Expression.Equal(
Expression.Property(parameter,colName),tenantExpr
)
)
);
var filter = Expression.Lambda(conditionalExpression,parameter);
entityType.SetQueryFilter(filter);
此外,您并不孤单,很多图书馆已经完成了这项任务,例如 ASP.NET Boilerplate
为了简化此类任务,我强烈建议使用表达式树可视化工具: https://github.com/agileobjects/ReadableExpressions https://github.com/zspitz/ExpressionTreeVisualizer