I'm using Entity Framework Core 2 in my application. I have a lot of nullable string columns in my database.
The problem is that I want to save empty strings as NULL in the database.
In old versions of EF, I used a IDbCommandInterceptor for implementing an interceptor, but in EF Core 2, I don't know how to write one ?
There is a new IDbCommandInterceptor interface that should be able to handle this, but it looks complicated.
A simple approach is be to write a function to remove empty strings, and then call it before data is saved within your DbContext class.
public void RemoveEmptyStrings()
{
// Look for changes
this.ChangeTracker.DetectChanges();
// Loop through each entity
foreach (var entity in this.ChangeTracker.Entries())
{
// Use reflection to find editable string properties
var properties = from p in entity.Entity.GetType().GetProperties()
where p.PropertyType == typeof(string)
&& p.CanRead
&& p.CanWrite
select p;
// Loop through each property and replace empty strings with null
foreach (var property in properties)
{
if (string.IsNullOrWhiteSpace(property.GetValue(entity.Entity, null) as string))
property.SetValue(entity.Entity, null, null);
}
}
}
Remember to override each version of SaveChanges(), SaveChanges(bool), SaveChangesAsync() in your DbContext class.
public override int SaveChanges()
{
// Replace empty strings with null
this.RemoveEmptyStrings();
// Continue with base functionality
return base.SaveChanges();
}
SaveChanges() seems to call SaveChanges(bool) and SaveChangesAsync(CancellationToken) seems to call SaveChangesAsync(bool, CancellationToken) under the hood so overriding the versions with only the bool seems to be sufficientBe careful with storing a different value in your DB than is in your domain object. Any code that touches this object will behave differently after it's hydrated from the DB.
If you always use String.IsNullOrEmpty(val), you will be ok, but there's guarantee that all code tests strings this way.
new ValueConverter<string, string>(v => v == "" ? null : v, v => v)with all these properties (columns).