毕设问题小记——No Dialect mapping for JDBC type:-1错误

　　为了实现在用户误操作后能够对数据进行修正，打算添加一个数据库管理功能，主要实现对数据表的查询和执行sql语句。费了半天功夫完成以后查询有的表数据正常显示，但是个别表出现如下错误：

No Dialect mapping for JDBC type: -1

　　意思显而易见：没有方言能够与JDBC类型-1映射。难道我数据库字段用了特殊类型，而hibernate不支持？百度之后找到很多同样错误，有的分析发现对于长度过大的varchar（LONGVARCHAR ）映射时会报这个错误，检查数据库发现这些表中都是用了text类型，应该就是这个原因。修改方法一般有两种：一是修改字段类型，二是扩展自定义方言。采用第二种方法修改如下：

添加自定义方言类：

package com.sxpt.util;

import java.sql.Types;

import org.hibernate.Hibernate;
import org.hibernate.dialect.MySQL5Dialect;

public class KtMySQL5Dialect extends MySQL5Dialect{
    public KtMySQL5Dialect(){
        super();
        this.registerHibernateType(Types.LONGVARCHAR, Hibernate.STRING.getName());
    }
}

hibernate.xml也要修改为对应方言：

        <property name="hibernate.dialect">
            com.sxpt.util.KtMySQL5Dialect
        </property>

下附java.sql.Types对应值，在出现错误时可根据值判断类型

public final static int BIT   =  -7;
public final static int TINYINT  =  -6;
public final static int SMALLINT =   5;
public final static int INTEGER  =   4;
public final static int BIGINT   =  -5;
public final static int FLOAT   =   6;
public final static int REAL   =   7;
public final static int DOUBLE   =   8;
public final static int NUMERIC  =   2;
public final static int DECIMAL  =   3;
public final static int CHAR  =   1;
public final static int VARCHAR  =  12;
public final static int LONGVARCHAR  =  -1;
public final static int DATE   =  91;
public final static int TIME   =  92;
public final static int TIMESTAMP  =  93;
public final static int BINARY  =  -2;
public final static int VARBINARY  =  -3;
public final static int LONGVARBINARY  =  -4;
public final static int NULL  =   0;
public final static int OTHER  = 1111;
public final static int JAVA_OBJECT         = 2000;
public final static int DISTINCT            = 2001;
public final static int STRUCT              = 2002;
public final static int ARRAY               = 2003;
public final static int BLOB                = 2004;
public final static int CLOB                = 2005;
public final static int REF                 = 2006;
public final static int DATALINK = 70;
public final static int BOOLEAN = 16;
public final static int ROWID = -8;
public static final int NCHAR = -15;
public static final int NVARCHAR = -9;
public static final int LONGNVARCHAR = -16;
public static final int NCLOB = 2011;
public static final int SQLXML = 2009;