JPA: 如何将字符串持久化到数据库字段中，输入 MYSQL Text

这个要求是用户可以写一篇文章，因此我为 mysql 数据库中的 content字段选择类型 Text。如何将 Java String转换为 MySQL Text

给你 Jim Tough

@Entity
public class Article implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;


private Long userId;


private String title;


private String content;


private Integer vote;


//Constructors, setters, getters, equals and hashcode
}

在我的 MYSQL 数据库中，content是 Text类型。我希望会有这样的 java.sql.Text，因为 java.sql.Blob是一个实际的类型，但遗憾的是，这并不存在

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最佳答案

Since you're using JPA, use the Lob annotation (and optionally the Column annotation). Here is what the JPA specification says about it:

9.1.19 Lob Annotation

A Lob annotation specifies that a persistent property or field should be persisted as a large object to a database-supported large object type. Portable applications should use the Lob annotation when mapping to a database Lob type. The Lob annotation may be used in conjunction with the Basic annotation. A Lob may be either a binary or character type. The Lob type is inferred from the type of the persistent field or property, and except for string and character-based types defaults to Blob.

So declare something like this:

@Lob
@Column(name="CONTENT", length=512)
private String content;

References

  • JPA 1.0 specification:
    • Section 9.1.19 "Lob Annotation"
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With @Lob I always end up with a LONGTEXTin MySQL.

To get TEXT I declare it that way (JPA 2.0):

@Column(columnDefinition = "TEXT")
private String text

Find this better, because I can directly choose which Text-Type the column will have in database.

For columnDefinition it is also good to read this.

EDIT: Please pay attention to Adam Siemions comment and check the database engine you are using, before applying columnDefinition = "TEXT".

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for mysql 'text': 

@Column(columnDefinition = "TEXT")
private String description;

for mysql 'longtext':

@Lob
private String description;

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