much more about basic types

documentation/src/main/asciidoc/introduction/Entities.adoc

@@ -379,8 +379,8 @@ The JPA specification defines a quite limited set of basic types:
 | Strings | `java.lang` | `String`
 | Arbitrary-precision numeric types | `java.math` | `BigInteger`, `BigDecimal`
 | Date/time types | `java.time` | `LocalDate`, `LocalTime`, `LocalDateTime`, `OffsetDateTime`, `Instant`
-| Deprecated date/time types | `java.util` | `Date`, `Calendar`
+| Deprecated date/time types 💀 | `java.util` | `Date`, `Calendar`
-| Deprecated JDBC date/time types | `java.sql` | `Date`, `Time`, `Timestamp`
+| Deprecated JDBC date/time types 💀 | `java.sql` | `Date`, `Time`, `Timestamp`
 | Binary and character arrays | | `byte[]`, `char[]`
 | UUIDs | `java.util` | `UUID`
 | Enumerated types | | Any `enum`
@@ -393,6 +393,13 @@ The JPA specification defines a quite limited set of basic types:
 We're begging you to use types from the `java.time` package instead of anything which inherits `java.util.Date`.
 ====
 
+[CAUTION]
+.Serialization is usually a bad idea
+====
+Serializing a Java object and storing its binary representation in the database is usually wrong.
+As we'll soon see, Hibernate has much better ways to handle complex Java objects.
+====
+
 The `@Basic` annotation explicitly specifies that an attribute is basic, but it's often not needed, since attributes are assumed basic by default.
 On the other hand, if an attribute cannot be null, use of `@Basic(optional=false)` is highly recommended.
 
@@ -404,7 +411,7 @@ String middleName; // may be null
 ----
 
 [TIP]
-.`optional` vs `nullable` in JPA
+.Should I use `optional=false` or `nullable=false` in JPA?
 ====
 There are two ways to mark a mapped column `not null` in JPA:
 
@@ -451,7 +458,7 @@ public static class BitSetConverter implements AttributeConverter<BitSet,byte[]>
 }
 ----
 
-On the other hand, if you don't set `autoapply=true`, then you must explicitly apply the converter using the `@Convert` annotation:
+On the other hand, if you _don't_ set `autoapply=true`, then you must explicitly apply the converter using the `@Convert` annotation:
 
 [source,java]
 ----
@@ -464,6 +471,88 @@ All this is nice, but it probably won't surprise you that Hibernate goes beyond
 
 === Compositional basic types
 
+Hibernate considers a "basic type" to be formed by the marriage of two objects:
+
+- a `JavaType`, which models the semantics of a certain Java class, and
+- a `JdbcType`, representing a SQL type which is understood by JDBC.
+
+An instance of `org.hibernate.type.descriptor.java.JavaType` represents a particular Java class.
+It is able to:
+
+- compare instances of the class to determine if an attribute of that class type is dirty (modified),
+- produce a useful hash code for an instance of the class,
+- coerce values to other types, and, in particular,
+- convert an instance of the class to one of several other equivalent Java representations at the request of its partner `JdbcType`.
+
+For example, `IntegerJavaType` knows how to convert an `Integer` or `int` value to the types `Long`, `BigInteger`, and `String`, among others.
+
+We may explicitly specify a Java type using the `@JavaType` annotation, but for the built-in ``JavaType``s this is never necessary.
+
+[source,java]
+----
+@JavaType(LongJavaType.class) // not needed, this is the default JavaType for long
+long currentTimeMillis;
+----
+
+For a user-written `JavaType`, the annotation is more useful:
+
+[source,java]
+----
+@JavaType(BitSetJavaType.class)
+BitSet bitSet;
+----
+
+Alternatively, the `@JavaTypeRegistration` may be used to register `BitSetJavaType` as the default `JavaType` for `BitSet`.
+
+A `org.hibernate.type.descriptor.jdbc.JdbcType` is able to read and write a single Java type from and to JDBC.
+
+For example, `VarcharJdbcType` takes care of:
+
+- writing Java strings to JDBC ``PreparedStatement``s by calling `setString()`, and
+- reading Java strings from JDBC ``ResultSet``s using `getString()`.
+
+By pairing `LongJavaType` with `VarcharJdbcType` in holy matrimony, we produce a basic type which maps ``Long``s and primitive ``longs``s to the SQL type `VARCHAR`.
+
+We may explicitly specify a JDBC type using the `@JdbcType` annotation.
+
+[source,java]
+----
+@JdbcType(VarcharJdbcType.class)
+long currentTimeMillis;
+----
+
+Alternatively, we may specify a JDBC type code:
+
+[source,java]
+----
+@JdbcTypeCode(Types.VARCHAR)
+long currentTimeMillis;
+----
+
+The `@JdbcTypeRegistration` annotation may be used to register a user-written `JdbcType` as the default for a given SQL type code.
+
+[NOTE]
+.JDBC types and JDBC type codes
+====
+The types defined by the JDBC specification are enumerated by the integer type codes in the class `java.sql.Types`.
+Each JDBC type is an abstraction of a commonly-available type in SQL.
+For example, `Types.VARCHAR` represents the SQL type `VARCHAR` (or `VARCHAR2` on Oracle).
+
+Since Hibernate understand more SQL types than JDBC, there's an extended list of integer type codes in the class `org.hibernate.type.SqlTypes`.
+====
+
+If a given `JavaType` does not know how to convert its instances to the type required by its partner `JdbcType`, we must help it out be providing a JPA `AttributeConverter` to perform the conversion.
+
+For example, to form a basic type using `LongJavaType` and `TimestampJdbcType`, we would provide an `AttributeConverter<Long,Timestamp>`.
+
+[source,java]
+----
+@JdbcType(TimestampJdbcType.class)
+@Convert(converter = LongToTimestampConverter.class)
+long currentTimeMillis;
+----
+
+
 === `equals()` and `hashCode()`
 
 Entity classes should override `equals()` and `hashCode()`. People new to