How can Hibernate map the SQL data-type nvarchar(m

问题:

I have a column in my SQL-2005 database that used to be a varchar(max), but it has been changed to an nvarchar(max).

Now I need to update my hibernate mapping file to reflect the change, and this is what it used to be:

<element type="text" column="Value"/>

When I try to run the application, the following error appears:

org.hibernate.HibernateException: Wrong column type in [Table] for column Value. Found: ntext, expected: text

What should I put in the 'type' attribute to correctly map the column as an nvarchar(max)?

I've tried setting the type to ntext, but hibernate didn't know what that was. I tried setting the type to string, but it treated string as a text type.

回答1:

What worked for me is to put the actual column definition in a @Column annotation:

    @Column(name="requestXml", columnDefinition = "ntext")
private String request;

回答2:

Found the answer at Tremend Tech Blog. You have to write your own SQLServerDialect class, it looks something like this:

public class SQLServerNativeDialect extends SQLServerDialect {
     public SQLServerNativeDialect() {
         super();
         registerColumnType(Types.VARCHAR, "nvarchar($l)");
         registerColumnType(Types.CLOB, "nvarchar(max)");
     }

    public String getTypeName(int code, int length, int precision, int scale) throws HibernateException {
        if(code != 2005) {
            return super.getTypeName(code, length, precision, scale);
        } else {
            return "ntext";
        }
    }
}

This class maps Hibernate's types to SQL types, so the class will map the nvarchar(max) SQL Data Type to Hibernate's CLOB data type.

The getTypeName method is used to return "ntext" when Hibernate asks about the data type with code 2005 (which looks like it's the nvarchar(max) data type).

Finally, you need to change your hibernate persistence dialect to this new SQLServerDialect class, which allows hibernate to translate data types into SQL data types.

回答3:

It can be fixed by @Nationalized annotation from hibernate, that marks a character data type like a nationalized variant (NVARCHAR, NCHAR, NCLOB, etc).

回答4:

I think it is registerColumnType(Types.VARCHAR, "nvarchar($l)"); // l like _l_ength, not 1.