Java – How to convert a Hibernate String column to an Enum

enumshibernatejavatypes

I currently have a simple String field in a Hibernate persisted class:

 private String font = "Times New Roman";

"Times New Roman" is the default value, so many stored objects have that data. For several reasons, I would like to convert this to an Enum:

 @Enumerated(EnumType.String)
 private FontEnum font = FontEnum.TIMES;

Hibernate uses Enum.valueOf(clazz, string) to convert the column data, which would fail on "Times New Roman" due to the spaces.

Googling suggests overriding Enum.valueOf() is impossible; do others know differently? Can I fool Enum.valueOf() to convert "Times New Roman" to FontEnum.TIMES?

Or, can I create a custom Hibernate converter like:

 public FontEnum legacyConverter(String old);

and add

 @Enumerated(EnumType.String)
 @Converter(Converters.legacyConverter()) // Does this exist?
 private FontEnum font = FontEnum.TIMES;

to my fields? I haven't seen anything like that.

I know a fallback method would be to add some pre-persist logic that slowly migrates the data to another column, but I'd like to avoid that.

Thank you – it's my first question on StackOverflow!

Best Answer

You can use a EnumUserType, see this Question.

Original Answer

In .NET it's rather ugly (until 4 or above):

StatusEnum MyStatus = (StatusEnum) Enum.Parse(typeof(StatusEnum), "Active", true);

I tend to simplify this with:

public static T ParseEnum<T>(string value)
{
    return (T) Enum.Parse(typeof(T), value, true);
}

Then I can do:

StatusEnum MyStatus = EnumUtil.ParseEnum<StatusEnum>("Active");

One option suggested in the comments is to add an extension, which is simple enough:

public static T ToEnum<T>(this string value)
{
    return (T) Enum.Parse(typeof(T), value, true);
}

StatusEnum MyStatus = "Active".ToEnum<StatusEnum>();

Finally, you may want to have a default enum to use if the string cannot be parsed:

public static T ToEnum<T>(this string value, T defaultValue) 
{
    if (string.IsNullOrEmpty(value))
    {
        return defaultValue;
    }

    T result;
    return Enum.TryParse<T>(value, true, out result) ? result : defaultValue;
}

Which makes this the call:

StatusEnum MyStatus = "Active".ToEnum(StatusEnum.None);

However, I would be careful adding an extension method like this to string as (without namespace control) it will appear on all instances of string whether they hold an enum or not (so 1234.ToString().ToEnum(StatusEnum.None) would be valid but nonsensical) . It's often be best to avoid cluttering Microsoft's core classes with extra methods that only apply in very specific contexts unless your entire development team has a very good understanding of what those extensions do.

C# – How to cast int to enum

From an int:

YourEnum foo = (YourEnum)yourInt;

From a string:

YourEnum foo = (YourEnum) Enum.Parse(typeof(YourEnum), yourString);

// The foo.ToString().Contains(",") check is necessary for enumerations marked with an [Flags] attribute
if (!Enum.IsDefined(typeof(YourEnum), foo) && !foo.ToString().Contains(","))
{
    throw new InvalidOperationException($"{yourString} is not an underlying value of the YourEnum enumeration.")
}

Update:

From number you can also

YourEnum foo = (YourEnum)Enum.ToObject(typeof(YourEnum) , yourInt);

Best Answer

Related Solutions

C# – Convert a string to an enum in C#

Original Answer

C# – How to cast int to enum

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