如何在实体框架核心中制作动态查询过滤器？

Question

I'm using do.net 6, and I want to make a global query filter in ef core to check my authentication ID dynamically, but the OnModelCreating runs just once in the lifecycle of ASP.net . Do you have any ideas how to do this?

This is my OnModelCreating method. DeletedAt type is DateTime? and my authentication ID is CompanyId . I get _companyId from the constructor and the type of it is long? . When a request is triggered, this ID fills, but my idea's problem is this method called at the startup of the project, At that time, the _companyId is null and never called again!

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    base.OnModelCreating(modelBuilder);

    modelBuilder.ApplyQueryFilters<IDeletedAt>(x => x.DeletedAt == null);
    modelBuilder.ApplyQueryFilters<IDeletedAtAndCompany>(x => x.DeletedAt == null && x.CompanyId == _companyId);
}

This is my ApplyQueryFilters method if you need:

public static void ApplyQueryFilters<T>(this ModelBuilder modelBuilder, Expression<Func<T, bool>> expression)
{
    foreach (var entityType in modelBuilder.Model.GetEntityTypes())
    {
        if (entityType.ClrType.GetInterface(typeof(T).Name) == null) continue;
        var newParam = Expression.Parameter(entityType.ClrType);
        var newBody = ReplacingExpressionVisitor
            .Replace(expression.Parameters.Single(), newParam, expression.Body);

        modelBuilder.Entity(entityType.ClrType).HasQueryFilter(Expression.Lambda(newBody, newParam));
    }
}

I think I need a new idea to resolve this issue.

Answer 1

Add the companyId to your Db Context then initialize it when you create the DbContext or when authenticate (you should have a DbContext peer session):

public class ApplicationDbContext
{
    ...

    public long? _companyId ; 
}

in your OnModelCreating add this default filter (adapt it to your case):

modelBuilder.Entity<YourEntity>().HasQueryFilter(b => EF.Property<string>(b, "companyId") == _companyId );

change the _companyId when needed.