如何将参数传递给hibernate AttributeConverter

Question

如果我有一个AttributeConverter在将输入保留在数据库中之前更改输入长度的方法，那么确保修改后的输入不超过该列允许的最大长度的正确方法是什么（无需在转换器中对其进行硬编码） ？

@Column(length = 1024)
@Convert(converter = MyConverter.class)
private String comment;

public class MyConverter implements AttributeConverter<String, String> {

   @Override
   public String convertToDatabaseColumn(String attribute) {
      return "hello world " + attribute;
   }
   ...
}

Answer 1

您可以使用实现接口的 hibernate自定义基本类型来实现您想要的DynamicParameterizedType。

下面您可以看到一个声明自定义类型的简单示例，该示例读取length@Column注释的属性。

import java.io.Serializable;
import java.lang.annotation.Annotation;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Types;
import java.util.Objects;
import java.util.Properties;

import javax.persistence.Column;

import org.hibernate.HibernateException;
import org.hibernate.engine.spi.SharedSessionContractImplementor;
import org.hibernate.usertype.DynamicParameterizedType;
import org.hibernate.usertype.UserType;

public class PersistableString implements UserType, DynamicParameterizedType
{
   private int sqlType;
   private int columnLength;

   public PersistableString()
   {
      this.sqlType = Types.VARCHAR;
   }

   @Override
   public void setParameterValues(Properties parameters)
   {
      ParameterType reader = (ParameterType) parameters.get(PARAMETER_TYPE);
      this.columnLength = getLength(reader);
   }

   private int getLength(ParameterType reader)
   {
      int length = -1; // default length
      for (Annotation annotation : reader.getAnnotationsMethod()){
         if (annotation instanceof Column) {
            length =  ((Column) annotation).length();
         }
      }
      return length;
   }

   @Override
   public int[] sqlTypes()
   {
      return new int[] {sqlType};
   }

   @Override
   public Class<?> returnedClass()
   {
      return String.class;
   }

   @Override
   public boolean equals(Object x, Object y) throws HibernateException
   {
      return Objects.equals(x, y);
   }

   @Override
   public int hashCode(Object x) throws HibernateException
   {
      return Objects.hashCode(x);
   }

   /*
      This method will be called when hibernate initializes your entity's
      field from the appropriate database table row
   */
   @Override
   public Object nullSafeGet(ResultSet rs,
         String[] names,
         SharedSessionContractImplementor session,
         Object owner) throws HibernateException, SQLException 
   {
      // you can use this.columnLength here
      return rs.getString(names[0]);
   }

   /*
      This method will be called when hibernate persists your entity's field
      to the appropriate database table row
   */
   @Override
   public void nullSafeSet(PreparedStatement st,
         Object value,
         int index,
         SharedSessionContractImplementor session) throws HibernateException, SQLException
   {
      // you can use this.columnLength here
      if (value == null) {
         st.setNull(index, sqlType);
      }
      else {
         String val = (String) value;
         st.setString(index, val);
      }
   }

   @Override
   public Object deepCopy(Object value) throws HibernateException
   {
      return value;
   }

   @Override
   public boolean isMutable()
   {
      return false;
   }

   @Override
   public Serializable disassemble(Object value) throws HibernateException
   {
      return Objects.toString(value);
   }

   @Override
   public Object assemble(Serializable cached, Object owner) throws HibernateException
   {
      return cached;
   }

   @Override
   public Object replace(Object original, Object target, Object owner) throws HibernateException
   {
      return original;
   }
}

和用法：

import org.hibernate.annotations.Type;


@Entity
@Table
public class Account
{

   @Column(name = "acc_name", length = 50)
   @Type(type = "com.example.hibernate.PersistableString")
   private String name;

   @Column(name = "acc_pass", length = 30)
   @Type(type = "com.example.hibernate.PersistableString")
   private String pass;

   @Column(name = "acc_email", length = 355)
   @Type(type = "com.example.hibernate.PersistableString")
   private String email;
}