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This article is about how mybatis passes in null values. The editor thinks it is very practical, so share it with you as a reference and follow the editor to have a look.

Mybatis passes in null value resolution

Two values are passed in the front end. If one of them is null, most of the time we are very confused. When we clearly pass in null, why is the if condition judgment invalid in the xml file of mybatis?

Public String getPersonInfo (@ PathParam ("Name") String Name, @ PathParam ("IDCard") String IDCard) dao layer public List getPersonInfo (@ Param ("name") String name, @ Param ("idcard") String idcard); xml file content

Every execution failed, and many people on the Internet said that it could be solved by adding @ param annotations to the dao layer and adding jdbcType types to the contents of the xml file, but it was not solved in the end.

In fact, there is another point ignored, that is, the null value passed in is actually a string null, which is not null at all, it is a string null.

If (Name = = null | | "null" .equalsIgnoreCase (Name)) {Name = null;} if (IDCard = = null | | "null" .equalsIgnoreCase (IDCard)) {IDCard = null;}

Problem solved!

Mybatis injection is always null

I have a very retarded problem today, for the record! Always remind yourself

Public int delExhibion (List ids) {Integer result = null; ExhibitionManager exhibitionManager = new ExhibitionManager (); for (String id: ids) {exhibitionManager.setId (id); exhibitionManager.setDelFlag ("1"); result + = exhibitionManagerMapper.delete (id);} return result;}

It is found that the null pointer exception is always reported when executing delete.

Then try to add a command to the parameter using: @ Param

Int delete (@ Param ("id") String id)

It still didn't work.

And then try to use: object to pass parameters, so it's time to inject it.

Int delete (Object dx)

It still didn't work.

Then try to use: Mybatis single parameter dynamic statement reference:

When our parameter is String, in the sql statement # {id} will go to the parameter we passed and call the getId () method to get the parameter. Obviously, String has no corresponding method, so an error has been reported. How to quote id here needs to be written as follows:

SELECT * FROM table AND id= # {id}

When a single Mybatis passes a parameter to a single parameter, you need to use _ parameter to reference this parameter in the sql statement

It still didn't work.

Finally, after a while, I had an epiphany of public int delExhibion (List ids) {Integer result = null; for (String id: ids) {result + = exhibitionManagerMapper.delete (id);} return result;} when I looked at the code.

Integer result I set the default value for him to null, and also let the object reuslt result + =

Add equals to use result to receive the result when the database operation is performed. This must be a null pointer.

I give Integer result = 0; set the default value to 0 and that won't happen!

Or result = assigning a value to result initialization will not report a null pointer exception! But this is wrong in my business. It's just that you won't make a mistake. But I can't get the number of successful execution I want.

Integer result = null;result = exhibitionManagerMapper.delete (id)

I'm really angry with myself. For the record! Always remind yourself

Public int delExhibion (List ids) {Integer result = 0; for (String id: ids) {result + = exhibitionManagerMapper.delete (id);} return result;} Thank you for reading! This is the end of the article on "how to pass in the null value of mybatis". I hope the above content can be of some help to you, so that you can learn more knowledge. if you think the article is good, you can share it out for more people to see!

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