Accessing

If you use field-based access, your JPA implementation uses reflection to read or write your entity attributes directly.
It also expects
that you place your mapping annotations on your entity attributes.
If you use property-based access, you need to annotate the getter methods of your entity attributes with the required mapping annotations.
Your JPA implementation then calls the getter and setter methods to access your entity attributes.

Collections

The persistent collections injected by Hibernate behave like ArrayList, HashSet, TreeSet, HashMap or TreeMap, depending on the interface
type.

java.util.List
java.util.Set
java.util.SortedSet
java.util.Map
java.util.SortedMap
java.util.Collection

Mapping to database examples

Mapping Annotations

types that I have used for mapping JSON or hashmap to mysql db
- VARCHAR(16384) : must have a max length to survive MariaDB DDL parser + hibernate validator
- LONGTEXT
- json
- longvarchar
- tinyblob
- longblob

map to blob

public class MapBlob {
    @ElementCollection
    @Column(columnDefinition = "BLOB NOT NULL")
    @MapKeyColumn(columnDefinition = "BLOB NOT NULL")
    private final Map<String, String> userFiles = new HashMap<>();
}

use collection table

with join

public class MapBlob {
    @ElementCollection
    @MapKeyColumn(name = "key")
    @Column(name = "value")
    @CollectionTable(name = "preference", joinColumns = @JoinColumn(name = "user_id"))
    private Map<String, String> preferences;
}

with more hibernate annotations

public class MapBlob {
    @CollectionOfElements(targetElement = java.lang.String.class)
    @JoinTable(name = "BOOK_CHAPTER", joinColumns = @JoinColumn(name = "BOOK_ID"))
    @MapKey(columns = @Column(name = "CHAPTER_KEY"))
    @Column(name = "CHAPTER")
    private Map<String, String> chapters;

}

with mapkeycolumn

field access

public class MapBlob {
    @ElementCollection(targetClass = String.class)
    @CollectionTable(name = "MAP")
    @MapKeyColumn(name = "key")
    @Column(name = "value")
    private Map<String, String> map;
}

property access

public class MapBlob {
    @ElementCollection(fetch = FetchType.EAGER)
    @CollectionTable(name = "TABLENAME")
    @MapKeyColumn(name = "KEY")
    @Column(name = "VALUE")
    public Map<String, String> getMap() {
        return _map;
    }
}

use json type class

in build.gradle

implementation("com.vladmihalcea:hibernate-types-52:2.21.1")

@TypeDefs({
        @org.hibernate.annotations.TypeDef(name = "JSON", typeClass = JsonBlobType.class),
        @org.hibernate.annotations.TypeDef(name = "JSONB", typeClass = JsonBinaryType.class)
})
public class Entity {
    @Type(type = "json")
    @Column(columnDefinition = "jsonb")
    private String preferences;
}

use hibernate types to map as blob and serializable

public class MapBlob {
    @org.hibernate.annotations.Type(
            type = "org.hibernate.type.SerializableToBlobType",
            parameters = {@Parameter(name = "classname", value = "java.util.HashMap")}
    )
    public Map<String, SentimentFrequencyCounts> getModelData() {
        return modelData;
    }
}

public class MapBlob {
    @org.hibernate.annotations.Type(type = "org.hibernate.type.SerializableType")
    public Map<String, SentimentFrequencyCounts> getModelData() {
        return modelData;
    }
}

save as string , map to map

public class User extends AbstractEntity {
    @JsonIgnore //This variable is going to be ignored whenever you send data to a client(ie. web browser)
    private String preferences;

    @Transient //This property is going to be ignored whenever you send data to the database
    @JsonProperty("preferences") //Whenever this property is serialized to the client, it is going to be named "perferences" instead "preferencesObj"
    private Preferences preferencesObj;

    public String getPreferences() {
        return new ObjectMapper().writeValueAsString(preferencesObj);
    }

    public void setPreferences(String preferences) {
        this.preferences   = preferences;
        this.preferncesObj = new ObjectMapper().readValue(preferences, Preferences.class);
    }

    public Prefrences getPreferencesObj() {
        return preferencesObj;
    }

    public void setPreferencesObj(Preferences preferencesObj) {
        this.preferencesObj = preferencesObj;
    }
}

use custom map

public class Location implements Serializable {

    private String country;

    private String city;

    //Getters and setters omitted for brevity

    @Override
    public String toString() {
        return "Location{" +
                "country='" + country + ' ' +
                ", city='" + city + ' ' +
                '}';
    }
}

Type Comparison

Hibernate Type	Database Type	JDBC Type	Type Registry
org.hibernate.type.StringType	string	VARCHAR	string, java.lang.String
org.hibernate.type.MaterializedClob	string	CLOB	materialized_clob
org.hibernate.type.TextType	string	LONGVARCHAR	text
org.hibernate.type.CharacterType	char, java.lang.Character	CHAR	char, java.lang.Character
org.hibernate.type.BooleanType	boolean	BIT	boolean, java.lang.Boolean
org.hibernate.type.NumericBooleanType	boolean	INTEGER, 0 is false, 1 is true	numeric_boolean
org.hibernate.type.YesNoType	boolean	CHAR, ‘N’/’n’ is false, ‘Y’/’y’ is true. The uppercase value is written to the database.	yes_no
org.hibernate.type.TrueFalseType	boolean	CHAR, ‘F’/’f’ is false, ‘T’/’t’ is true. The uppercase value is written to the database.	true_false
org.hibernate.type.ByteType	byte, java.lang.Byte	TINYINT	byte, java.lang.Byte
org.hibernate.type.ShortType	short, java.lang.Short	SMALLINT	short, java.lang.Short
org.hibernate.type.IntegerTypes	int, java.lang.Integer	INTEGER	int, java.lang.Integer
org.hibernate.type.LongType	long, java.lang.Long	BIGINT	long, java.lang.Long
org.hibernate.type.FloatType	float, java.lang.Float	FLOAT	float, java.lang.Float
org.hibernate.type.DoubleType	double, java.lang.Double	DOUBLE	double, java.lang.Double
org.hibernate.type.BigIntegerType	java.math.BigInteger	NUMERIC	big_integer
org.hibernate.type.BigDecimalType	java.math.BigDecimal	NUMERIC	big_decimal, java.math.bigDecimal
org.hibernate.type.TimestampType	java.sql.Timestamp	TIMESTAMP	timestamp, java.sql.Timestamp
org.hibernate.type.TimeType	java.sql.Time	TIME	time, java.sql.Time
org.hibernate.type.DateType	java.sql.Date	DATE	date, java.sql.Date
org.hibernate.type.CalendarType	java.util.Calendar	TIMESTAMP	calendar, java.util.Calendar
org.hibernate.type.CalendarDateType	java.util.Calendar	DATE	calendar_date
org.hibernate.type.CurrencyType	java.util.Currency	VARCHAR	currency, java.util.Currency
org.hibernate.type.LocaleType	java.util.Locale	VARCHAR	locale, java.utility.locale
org.hibernate.type.TimeZoneType	java.util.TimeZone	VARCHAR (Using the TimeZone ID)	timezone, java.util.TimeZone
org.hibernate.type.UrlType	java.net.URL	VARCHAR	url, java.net.URL
org.hibernate.type.ClassType	java.lang.Class	VARCHAR (Using the class name)	class, java.lang.Class
org.hibernate.type.BlobType	java.sql.Blob	BLOB	blog, java.sql.Blob
org.hibernate.type.ClobType	java.sql.Clob	CLOB	clob, java.sql.Clob
org.hibernate.type.BinaryType	primitive byte[]	VARBINARY	binary, byte[]
org.hibernate.type.MaterializedBlobType	primitive byte[]	BLOB	materized_blob
org.hibernate.type.ImageType	primitive byte[]	LONGVARBINARY	image
org.hibernate.type.BinaryType	java.lang.Byte[]	VARBINARY	wrapper-binary
org.hibernate.type.CharArrayType	char[]	VARCHAR	characters, char[]
org.hibernate.type.CharacterArrayType	java.lang.Character[]	VARCHAR	wrapper-characters, Character[], java.lang.Character[]
org.hibernate.type.UUIDBinaryType	java.util.UUID	BINARY	uuid-binary, java.util.UUID
org.hibernate.type.UUIDCharType	java.util.UUID	CHAR, VARCHAR	uuid-char
org.hibernate.type.PostgresUUIDType	java.util.UUID	PostgreSQL UUID	pg-uuid
org.hibernate.type.SerializableType	Implementors of java.lang.Serializable	VARBINARY	Unlike the other value types, multiple instances of this type are registered. It is registered once under java.io.Serializable and registered under the specific java.io.Serializable implementation class names