Dynamic SQL does not work for checking parameter is null.

[Ming Xia]

Hi,

I was trying to use mybatis dynamic sql, but seems it does not produce correct sql statement when checking if a specific parameter is null. Even `record.description==null`, the generated sql still include set description=?, and the record in db is updated with description=`null`, even it was not null before updating. Any idea on this problem, or it is a bug of MyBatis? My Mybatis version is 3.4.0.

Thanks,

Ming

@Update({
    "<script>",
      "update city",
      "<set>",
        "<if test='#{description} != null'>description = #{description,jdbcType=VARCHAR},</if>",
      "</set>",
      "where name = #{name,jdbcType=VARCHAR}",
    "</script>"
})
@Override
int update(CityDO record);

My `CityDO` has only `name` and `description` field, and I verified that the description field is null before passing it to the `update` method.

[Guy Rouillier]

Expressions within the tags - <if>, in this case - are Java expressions (specifically, OGNL expressions), not parameter expressions. So, the proper test here would be:

<pre>

<if test='description != null'>

description = #{description,jdbcType=VARCHAR},

</if>

</pre>

You don't have to have the entire clause on a single line, though you may if you prefer.

I think it's a little more readable to have the tags on separate lines from the text within the tags.

--

Guy Rouillier

[Ming Xia]

Verified and it works, thank you Guy, appreciate your help.

Best,

Ming

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