Spring JPA-OneToOne不从辅助表中选择数据-MySQL

Question

New to spring data and have an issue I can't resolve. Have a mySql database and am trying to use OneToOne to get data from a table using a foreign key.

Table 1 - location
   id      int(11) pk nn UQ
   zipcode varchar(11) NN UQ
   city    varchar(45) NN
   lat     Double      NN
   lon     Double      NN

Table 2 - weather
   id           INT(11)  PK NN
   location_id  INT(11)  NN
   desc         varchar(45)  NN
Foreign Key name fk_location_id  referenced table location column location_id referenced column id - pointed to location column id.`

WeatherData.java column definition @OneToOne (fetch = FetchType.LAZY) @JoinColumn(name="fk_location_id") private LocationData location;

Code performing the query: for (WeatherData weather : repository.findAll()) { log.info(weather.toString()); } for (WeatherData weather : repository.findAll()) { log.info(weather.toString()); }

` Set a break point in the code above to the log.info line and look at the weather record returned. The location value is null. Have tried setting the OneToOne column name to id without success.

What am I doing wrong?

Answer 1

I'd try the following 3 things:

1. set the value in your @JoinColumn to the name of the FK column.
2. make sure your FK entity class (LocationData) has a properly formatted @OneToOne annotation. The mappedBy value is the name of the field in WeatherData that has the @OneToOne and @JoinColumn annotations.
3. make sure your entity classes are annotated as entities (via @Entity).

Using the this site's example , your weather table would be the book table, and location would be the book_detail table. That being said, there are a few annotations to make sure you're using. First of all, make sure your entity classes are labeled as so. ie:

 @Entity
 @Table(name = "weather")
 public class WeatherData {

If your entity class and table have the same name, then you can omit the @Table annotation; however, I like to always add it as I consider it good practice. Make sure you annotate all your entity classes, not just WeatherData. Now, as for the location_id, your @JoinColumn should refer to the column in your table.

@OneToOne (fetch = FetchType.LAZY)
@JoinColumn(name="location_id")
private LocationData location;

Then, in your LocationData class, you need to annotate the locationId field with @OneToOne as well.

@OneToOne(mappedBy = "location")
private WeatherData weather;

Take a look at the linked article for more info. I hope this helps.

Answer 2

Fixed the issue with the following changes:

@OneToOne (fetch = FetchType.EAGER) @JoinColumn(name="location_id") private LocationData location;

and fixed incorrect data type defined as a int when it should have been a string in the locationdata class. Also had an issue with a double set as a int in the locationdata toString method.