解决Conversion接口ToDB() ([]byte, error)方法返回*Type值为nil时,数据类型为[]byte(nil)的…

[peihexian]

解决字段类型为*Type，值为nil时，插入数据变为""的bug。解决update操作时，*Type类型字段的值为nil时，数据值变成[]byte(nil)的bug，正确的情况应该是interface(nil)。

[codecov-io]

Codecov Report

Merging #1296 into master will decrease coverage by 0.08%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #1296      +/-   ##
==========================================
- Coverage   57.41%   57.33%   -0.09%     
==========================================
  Files          44       44              
  Lines        7912     7823      -89     
==========================================
- Hits         4543     4485      -58     
+ Misses       2806     2781      -25     
+ Partials      563      557       -6

Impacted Files	Coverage Δ
statement.go	68.05% <0%> (+0.19%)	⬆️
session_convert.go	22.19% <0%> (-0.1%)	⬇️
rows.go	52.38% <0%> (-3.76%)	⬇️
helpers.go	57.41% <0%> (-2.32%)	⬇️
tag.go	77.09% <0%> (-2.22%)	⬇️
engine.go	61.53% <0%> (-1.06%)	⬇️
session_update.go	56.44% <0%> (-0.18%)	⬇️
session_insert.go	56.84% <0%> (-0.12%)	⬇️
dialect_oracle.go	0% <0%> (ø)	⬆️
dialect_postgres.go	76.11% <0%> (+0.15%)	⬆️
... and 6 more

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[peihexian]

because Conversion interface ToDB method return []byte type data,when field value is nil,ToDB() method will return []byte(nil) (is goland it's displayed []uint8(nil)),but db engine can't convert that type to interface(nil),then insert or update operation will be failed. now ,val=data fixed to if nil==data { val=nil } ,when data is nil,val type is interface(nil),db engine will translate it to NULL，then bug fixed.
if nil==data return nil,nil same as above。

[peihexian]

为什么不给合并？是不是没有说清楚？ 自定义类型例如 type MyTime time.Time 这种，如果在struct里面使用时是指针类型的话，例如 type Student struct {
Name string
Birthday *MyTime
} 这种情况，需要为MyTime去实现Conversion接口，向数据库写入是ToDB方面，该方法返回值类型是[]byte ,error，如果Birthday字段用户并没有输入数据值的话，也就是Birthday字段值为nil的话，ToDB方法只能返回nil，但是因为已经限定了数据类型是[]byte，所以数据库引擎在执行时给该字段赋值为[]byte(nil)这样的参数数据，这种[]byte(nil)数据库引擎是不认的，但是改为interface(nil)的话就可以正确识别为NULL，所以加了上面改动那些代码，不知道用中文说明白没有？

[lunny]

Could you add some tests?