1. You can restrict the comparison to specified key columns. The Compare stage does not change the table definition, partitioning, or content of the records in either input data set. It transfers both data sets intact to a single output data set generated by the stage. The comparison.
2. Specify the column of the comparison table with unique keys i.e. By design contains no duplicate keys as the Generated key column. A generated key column indicates which row of a set containing identical primary keys is to be used in the comparison. This provides a method of handling duplicate keys in the comparison table.

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Jun 25, 2012 I was just evaluating the usage of Table Comparison with Key Generation. What I know is that Key Generation is used to generate new keys for records flagged with 'INSERT'. What happens to the Generated Key column when the input is from TableComparison, for the records flagged other than 'INSERT'? Thanks and Regards, Bhupendra. We are going to see that it is performing a full index scan over the first table, and that the generated column has never been executed. That is how we can go from an inconsistent result of three seconds, to a consistent result of 2.31 seconds, to finally reach a performant query using the faster time of 1.60 seconds.

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To delta load a table which has a surrogate key as primary key you simply combine Table Comparison with Key Generation Transform. Behind the scenes, some not so obvious things go on.

The flow itself is simple.

The secret is the Table Comparison Transform, that perform the lookup on the target table to get the current status. With this lookup, it can read and will output all the columns, even if they are not part of the input schema. An example is the surrogate key of the target table. The Table Comparison does get the logical primary key as input, tries to find the matching row in the comparison (target) table and if found, will get all the missing column values as well like the corresponding KEY_ID.

The only thing to watchout is, if using the row-by-row setting of the Transform, the compare table has to have an index on the logical(!!) primary key - CUSTOMER_ID in this example.

Generated Column Sql

Now the Key Generation Transform gets insert and update rows but will overwrite the KEY_ID column only for rows with OP code of insert - rows that do not have a KEY_ID yet.

And at then end, the target table loader does execute the insert or the update statement. For the update statement, it needs to know what the physical primary key is, so make sure the target table got imported with primary key column(s) into the DI repo.

Every JPA entity is required to have a field which maps to primary key of the database table. Such field must be annotated with @Id.

Simple vs Composite primary keys

A simple primary key consists of a single Java field which maps to a single table column.
A composite primary key consists of multiple Java fields which individually map to separate columns.

Supported types for a primary key

A simple primary key field or one of the composite primary key field should be one of the following types:

• Any Java primitive type
• any Any primitive wrapper type
• java.lang.String
• java.util.Date
• java.sql.Date
• java.math.BigDecimal
• java.math.BigInteger

In this tutorial we are going to focus on generation strategies of simple primary key.

Generate rsa public private key pair openssl. / ( )?,&. Only the public key is sent to a Certificate Authority and included in the SSL certificate, and it works together with your private key to encrypt the connection. Certificate signing requests (CSR) are generated with a pair of keys – a public and private key.

@GeneratedValue Annotation

This annotation defines the types of primary key generation strategies. If this annotation is not used then application is responsible to populate and manage @Id field values itself.

The use of the GeneratedValue annotation is only required to be supported for simple primary keys.

GenerationType enum defines four strategies: Generation Type . TABLE, Generation Type. SEQUENCE, Generation Type. IDENTITY and Generation Type. AUTO. Let's understand them with examples.

GenerationType.SEQUENCE

With this strategy, underlying persistence provider must use a database sequence to get the next unique primary key for the entities.

We have created the following Util class to reuse the code for other examples.

Also, in the persistence.xml, we have created four persistence-unit, so that we can try four GenerationType independently. We are using Hibernate as persistence provider.

Let's create main class to try out Entity1 key generation.

Output

Above output shows one table MYENTITY1 and one sequence HIBERNATE_SEQUENCE are created.

GenerationType.TABLE

With this strategy, underlying persistence provider must use a database table to generate/keep the next unique primary key for the entities.

Output

This time no sequence is generated, instead an additional table named 'HIBERNATE_SEQUENCES' is created to maintain primary key sequence.

GenerationType.IDENTITY

This GenerationType indicates that the persistence provider must assign primary keys for the entity using a database identity column. IDENTITY column is typically used in SQL Server. This special type column is populated internally by the table itself without using a separate sequence. If underlying database doesn't support IDENTITY column or some similar variant then the persistence provider can choose an alternative appropriate strategy. In this examples we are using H2 database which doesn't support IDENTITY column.

Output

Above output shows that a sequence is used for primary keys.

GenerationType.AUTO

This GenerationType indicates that the persistence provider should automatically pick an appropriate strategy for the particular database. This is the default GenerationType, i.e. if we just use @GeneratedValue annotation then this value of GenerationType will be used.

Waters Column Comparison

Output

Above output shows that a sequence is used for primary keys.

When @GeneratedValue not used

Generated Key Column In Table Comparison Excel

If we don't use @GeneratedValue annotation at all, then we have to populate the unique primary keys ourselves. In this example, we are simply assigning it to the value returned from System.nanoTime()

Output

Mysql Generated Column Index

Above output shows that a no sequence or extra table were generated.

Example Project

Dependencies and Technologies Used:

Generated Key Column In Table Comparison Chart

• h2 1.4.193: H2 Database Engine.
• hibernate-core 5.2.8.Final: The core O/RM functionality as provided by Hibernate.
  Implements javax.persistence:javax.persistence-api version 2.1
• JDK 1.8
• Maven 3.3.9