Highperformance Java Persistence Pdf 12

Highperformance Java Persistence Pdf 12

LINK ::: https://tiurll.com/2tfZ33

Vlad Mihalcea is a Java Champion and one of the top Hibernate ORM project committers. He created the Hypersistence Optimizer tool, which scans your application configuration and mappings and tells you what changes you need to make to speed up your data access layer.

Writing a book is difficult, but writing a book about performance and persistence is a real challenge. If you want to understand how locking, sharding, replication, database concurrency control work, then this book is for you. Vlad gives you plenty of tips and tricks on Hibernate, helping you diagnose your performance issues (e.g. mapping, fetching, or caching). I learn a lot by reading his book and I highly recommend it if you use relational databases and ORM tools such as Hibernate.

Good books on persistence are few and far between. This is something else - it's deeply researched but also entirely practical. I'm basically using it as a reference for everything SQL. Plus, the transaction chapter is a must read.

Behind the scenes, the Hibernate Session wraps a JDBC java.sql.Connection and acts as a factory for org.hibernate.Transaction instances.It maintains a generally \"repeatable read\" persistence context (first level cache) of the application domain model.

Ultimately the application domain model is the central character in an ORM.They make up the classes you wish to map. Hibernate works best if these classes follow the Plain Old Java Object (POJO) / JavaBean programming model.However, none of these rules are hard requirements.Indeed, Hibernate assumes very little about the nature of your persistent objects. You can express a domain model in other ways (using trees of java.util.Map instances, for example).

Strictly speaking, a basic type is denoted by the javax.persistence.Basic annotation.Generally speaking, the @Basic annotation can be ignored, as it is assumed by default.Both of the following examples are ultimately the same.

We said before that a Hibernate type is not a Java type, nor an SQL type, but that it understands both and performs the marshalling between them.But looking at the basic type mappings from the previous examples,how did Hibernate know to use its org.hibernate.type.StringType for mapping for java.lang.String attributes,or its org.hibernate.type.IntegerType for mapping java.lang.Integer attributes

As an example, take a String attribute such as we saw before with Product#sku.Since there was no explicit type mapping, Hibernate looks to the BasicTypeRegistry to find the registered mapping for java.lang.String.This goes back to the \"BasicTypeRegistry key(s)\" column we saw in the tables at the start of this chapter.

Hibernate makes it relatively easy for developers to create their own basic type mappings type.For example, you might want to persist properties of type java.util.BigInteger to VARCHAR columns, or support completely new types.

The AbstractSingleColumnStandardBasicType requires an sqlTypeDescriptor and a javaTypeDescriptor.The sqlTypeDescriptor is VarcharTypeDescriptor.INSTANCE because the database column is a VARCHAR.On the Java side, we need to use a BitSetTypeDescriptor instance which can be implemented like this:

The original JPA-compliant way to map enums was via the @Enumerated or @MapKeyEnumerated for map keys annotations, working on the principle that the enum values are stored according to one of 2 strategies indicated by javax.persistence.EnumType:

While the java.sql classes define a direct association to the SQL Date/Time data types,the java.util or java.time properties need to explicitly mark the SQL type correlation with the @Temporal annotation.This way, a java.util.Date or a java.util.Calendar can be mapped to either an SQL DATE, TIME or TIMESTAMP type.

By default, Hibernate is going to use the PreparedStatement.setTimestamp(int parameterIndex, java.sql.Timestamp) orPreparedStatement.setTime(int parameterIndex, java.sql.Time x) when saving a java.sql.Timestamp or a java.sql.Time property.

With this configuration property in place, Hibernate is going to call the PreparedStatement.setTimestamp(int parameterIndex, java.sql.Timestamp, Calendar cal) orPreparedStatement.setTime(int parameterIndex, java.sql.Time x, Calendar cal), where the java.util.Calendar references the time zone provided via the hibernate.jdbc.time_zone property.

An entity models a database table.The identifier uniquely identifies each row in that table.By default, the name of the table is assumed to be the same as the name of the entity.To explicitly give the name of the table or to specify other information about the table, we would use the javax.persistence.Table annotation.

The composite identifier must be represented by a \"primary key class\".The primary key class may be defined using the javax.persistence.EmbeddedId annotation (see Composite identifiers with @EmbeddedId),or defined using the javax.persistence.IdClass annotation (see Composite identifiers with @IdClass).

Identifier value generation is indicated using the javax.persistence.GeneratedValue annotation.The most important piece of information here is the specified javax.persistence.GenerationType which indicates how values will be generated.

This can mess up extended persistence contexts (long conversations).Because of the runtime imposition/inconsistency, Hibernate suggests other forms of identifier value generation be used (e.g. SEQUENCE).

The unidirectional associations are not very efficient when it comes to removing child entities.In the example above, upon flushing the persistence context, Hibernate deletes all database rows from the link table (e.g. Person_Phone) that are associated with the parent Person entity and reinserts the ones that are still found in the @OneToMany collection.

Unlike the unidirectional @OneToMany, the bidirectional association is much more efficient when managing the collection persistence state.Every element removal only requires a single update (in which the foreign key column is set to NULL), and,if the child entity lifecycle is bound to its owning parent so that the child cannot exist without its parent,then we can annotate the association with the orphanRemoval attribute and dissociating the child will trigger a delete statement on the actual child table row as well.

Hibernate uses its own collection implementations which are enriched with lazy-loading, caching or state change detection semantics.For this reason, persistent collections must be declared as an interface type.The actual interface might be java.util.Collection, java.util.List, java.util.Set, java.util.Map, java.util.SortedSet, java.util.SortedMap or even other object types (meaning you will have to write an implementation of org.hibernate.usertype.UserCollectionType).

From a theoretical perspective, this just follows good design principles.From a practical perspective, Hibernate (like other persistence providers) will use their own collection implementations which conform to the Java Collections Framework interfaces.

From a relational database perspective, associations are defined by the foreign key side (the child-side).With value type collections, only the entity can control the association (the parent-side), but for a collection of entities, both sides of the association are managed by the persistence context.

A java.util.Map is a ternary association because it requires a parent entity, a map key, and a value.An entity can either be a map key or a map value, depending on the mapping.Hibernate allows using the following map keys:

The discriminator column contains marker values that tell the persistence layer what subclass to instantiate for a particular row.Hibernate Core supports the following restricted set of types as discriminator column: String, char, int, byte, short, boolean(including yes_no, true_false).

The enum DiscriminatorType used in javax.persistence.DiscriminatorColumn only contains the values STRING, CHAR and INTEGER which means that not all Hibernate supported types are available via the @DiscriminatorColumn annotation.You can also use @DiscriminatorFormula to express in SQL a virtual discriminator column.This is particularly useful when the discriminator value can be extracted from one or more columns of the table.Both @DiscriminatorColumn and @DiscriminatorFormula are to be set on the root entity (once per persisted hierarchy).

In JPA, we are ultimately interested in bootstrapping a javax.persistence.EntityManagerFactory instance.The JPA specification defines two primary standardized bootstrap approaches depending on how the application intends to access the javax.persistence.EntityManager instances from an EntityManagerFactory.

For compliant container-bootstrapping, the container will build an EntityManagerFactory for each persistent-unit defined in the META-INF/persistence.xml configuration fileand make that available to the application for injection via the javax.persistence.PersistenceUnit annotation or via JNDI lookup.

For compliant application-bootstrapping, rather than the container building the EntityManagerFactory for the application, the application builds the EntityManagerFactory itself using the javax.persistence.Persistence bootstrap class.The application creates an EntityManagerFactory by calling the createEntityManagerFactory method:

An object/relational mapping XML file named orm.xml may be specified in the META-INF directory in the root of the persistence unit or in the META-INF directory of any jar file referenced by the persistence.xml.

Both the org.hibernate.Session API and javax.persistence.EntityManager API represent a context for dealing with persistent data.This concept is called a persistence context.Persistent data has a state in relation to both a persistence context and the underlying database.

the entity has just been instantiated and is not associated with a persistence context.It has no persistent representation in the database and typically no identifier value has been assigned (unless the assigned generator was used).

Historically Hibernate only supported diff-based dirty calculation for determining which entities in a persistence context have changed.This essentially means that Hibernate would keep track of the last known state of an entity in regards to the database (typically the last read or write).Then, as part of flushing the persistence context, Hibernate would walk every entity associated with the persistence context and check its current state against that \"last known database state\".This is by far the most thorough approach to dirty checking because it accounts for data-types that can change their internal state (java.util.Date is the prime example of this).However, in a persistence context with a large number of associated entities, it can also be a performance-inhibiting approach. 153554b96e

https://www.sellcgs.com/group/mysite-231-group/discussion/ed724bb1-cd50-4447-84f1-a099e14c6fd3

https://www.dwplc.net/forum/untitled-category/sag-salim-1-tek-parca-720p-mkv

https://www.phi-vietnamese.com/forum/questions-answers/clamxav-3-0-15-build-8328-crack-exclusive-free-download