The sql: component allows you to work with databases using JDBC queries. The difference between this component and JDBC component is that in case of SQL the query is a property of the endpoint and it uses message payload as parameters passed to the query.
This component uses
spring-jdbc behind the scenes for the actual SQL handling.
Maven users will need to add the following dependency to their
pom.xml for this component:
The SQL component also supports:
- a JDBC based repository for the Idempotent Consumer EIP pattern. See further below.
- a JDBC based repository for the Aggregator EIP pattern. See further below.
The SQL component uses the following endpoint URI notation:
From Camel 2.11 onwards you can use named parameters by using :
#name_of_the_parameter style as shown:
When using named parameters, Camel will lookup the names from, in the given precedence:
1. from message body if its a
2. from message headers
If a named parameter cannot be resolved, then an exception is thrown.
From Camel 2.14 onward you can use Simple expressions as parameters as shown:
Notice that the standard
? symbol that denotes the parameters to an SQL query is substituted with the
# symbol, because the
? symbol is used to specify options for the endpoint. The
? symbol replacement can be configured on endpoint basis.
You can append query options to the URI in the following format,
Camel 2.7.5, 2.8.4 and 2.9: Execute SQL batch update statements. See notes below on how the treatment of the inbound message body changes if this is set to
Deprecated and will be removed in Camel 3.0: Reference to a
Camel 2.11: Reference to a
Camel 2.4: Specifies a character that will be replaced to
Sets additional options on the Spring
Camel 2.11: Whether to allow using named parameters in the queries.
Camel 2.11: SQL consumer only: Allows to plugin to use a custom
Camel 2.11: Allows to plugin to use a custom
Camel 2.11: SQL consumer only: Delay in milliseconds between each poll.
Camel 2.11: SQL consumer only: Milliseconds before polling starts.
Camel 2.11: SQL consumer only: Set to
Camel 2.11: SQL consumer only: An integer value to define the maximum number of messages to gather per poll. By default, no maximum is set.
Camel 2.11: SQL consumer only: If
Camel 2.11: SQL consumer only: Whether to route a single empty Exchange if there was no data to poll.
Camel 2.11: SQL consumer only: After processing each row then this query can be executed, if the Exchange was processed successfully, for example to mark the row as processed. The query can have parameter.
Camel 2.11: SQL consumer only: After processing each row then this query can be executed, if the Exchange failed, for example to mark the row as failed. The query can have parameter.
Camel 2.11: SQL consumer only: After processing the entire batch, this query can be executed to bulk update rows etc. The query cannot have parameters.
Camel 2.11: SQL consumer only: If using
Camel 2.11: SQL consumer only: If using
Camel 2.11: SQL producer only: If enabled then the
Camel 2.11.1: The separator to use when parameter values is taken from message body (if the body is a String type), to be inserted at # placeholders. Notice if you use named parameters, then a
Camel 2.12.0: Make the output of consumer or producer to
From Camel 2.14.1 onwards the SelectList also supports mapping each row to a Java object as the SelectOne does (only step c).
Camel 2.12.0: Specify the full package and class name to use as conversion when
Camel 2.15: To store the result as a header instead of the message body. This allows to preserve the existing message body as-is.
Camel 2.11.2/2.12.0 If set greater than zero, then Camel will use this count value of parameters to replace instead of querying via JDBC metadata API. This is useful if the JDBC vendor could not return correct parameters count, then user may override instead.
Camel 2.12.0 If set, will ignore the results of the SQL query and use the existing IN message as the OUT message for the continuation of processing
Treatment of the message body
The SQL component tries to convert the message body to an object of
java.util.Iterator type and then uses this iterator to fill the query parameters (where each query parameter is represented by a
# symbol (or configured placeholder) in the endpoint URI). If the message body is not an array or collection, the conversion results in an iterator that iterates over only one object, which is the body itself.
For example, if the message body is an instance of
java.util.List, the first item in the list is substituted into the first occurrence of
# in the SQL query, the second item in the list is substituted into the second occurrence of
#, and so on.
batch is set to
true, then the interpretation of the inbound message body changes slightly – instead of an iterator of parameters, the component expects an iterator that contains the parameter iterators; the size of the outer iterator determines the batch size.
Result of the query
select operations, the result is an instance of
List<Map<String, Object>> type, as returned by the JdbcTemplate.queryForList() method. For
update operations, the result is the number of updated rows, returned as an
By default, the result is placed in the message body. If the outputHeader parameter is set, the result is placed in the header. This is an alternative to using a full message enrichment pattern to add headers, it provides a concise syntax for querying a sequence or some other small value into a header. It is convenient to use outputHeader and outputType together:
update operations, the SQL Component stores the update count in the following message headers:
The number of rows updated for
The number of rows returned for
Camel 2.8: Query to execute. This query takes precedence over the query specified in the endpoint URI. Note that query parameters in the header are represented by a
insert operations, the SQL Component stores the rows with the generated keys and number of these rown in the following message headers (Available as of Camel 2.12.4, 2.13.1):
|The number of rows in the header that contains generated keys.|
|Rows that contains the generated keys (a list of maps of keys).|
Available as of Camel 2.12.4, 2.13.1 and 2.14
If you insert data using SQL INSERT, then the RDBMS may support auto generated keys. You can instruct the SQL producer to return the generated keys in headers.
To do that set the header
CamelSqlRetrieveGeneratedKeys=true. Then the generated keys will be provided as headers with the keys listed in the table above.
You can see more details in this unit test.
You can now set a reference to a
DataSource in the URI directly:
In the sample below we execute a query and retrieve the result as a
List of rows, where each row is a
Map<String, Object and the key is the column name.
First, we set up a table to use for our sample. As this is based on an unit test, we do it in java:
The SQL script
createAndPopulateDatabase.sql we execute looks like as described below:
Then we configure our route and our
sql component. Notice that we use a
direct endpoint in front of the
sql endpoint. This allows us to send an exchange to the
direct endpoint with the URI,
direct:simple, which is much easier for the client to use than the long
sql: URI. Note that the
DataSource is looked up up in the registry, so we can use standard Spring XML to configure our
And then we fire the message into the
direct endpoint that will route it to our
sql component that queries the database.
We could configure the
DataSource in Spring XML as follows:
Using named parameters
Available as of Camel 2.11
In the given route below, we want to get all the projects from the projects table. Notice the SQL query has 2 named parameters, :#lic and :#min.
Camel will then lookup for these parameters from the message body or message headers. Notice in the example above we set two headers with constant value
for the named parameters:
Though if the message body is a
java.util.Map then the named parameters will be taken from the body.
Using expression parameters
Available as of Camel 2.14
In the given route below, we want to get all the project from the database. It uses the body of the exchange for defining the license and uses the value of a property as the second parameter.
Using the JDBC based idempotent repository
Available as of Camel 2.7: In this section we will use the JDBC based idempotent repository.
First we have to create the database table which will be used by the idempotent repository. For Camel 2.7, we use the following schema:
In Camel 2.8, we added the createdAt column:
We recommend to have a unique constraint on the columns processorName and messageId. Because the syntax for this constraint differs for database to database, we do not show it here.
Second we need to setup a
javax.sql.DataSource in the spring XML file:
And finally we can create our JDBC idempotent repository in the spring XML file as well:
Customize the JdbcMessageIdRepository
Starting with Camel 2.9.1 you have a few options to tune the
org.apache.camel.processor.idempotent.jdbc.JdbcMessageIdRepository for your needs:
Defines whether or not Camel should try to create the table if it doesn't exist.
SELECT 1 FROM CAMEL_MESSAGEPROCESSED WHERE 1 = 0
This query is used to figure out whether the table already exists or not. It must throw an exception to indicate the table doesn't exist.
CREATE TABLE CAMEL_MESSAGEPROCESSED (processorName VARCHAR(255), messageId VARCHAR(100), createdAt TIMESTAMP)
The statement which is used to create the table.
SELECT COUNT(*) FROM CAMEL_MESSAGEPROCESSED WHERE processorName = ? AND messageId = ?
The query which is used to figure out whether the message already exists in the repository (the result is not equals to '0'). It takes two parameters. This first one is the processor name (
INSERT INTO CAMEL_MESSAGEPROCESSED (processorName, messageId, createdAt) VALUES (?, ?, ?)
The statement which is used to add the entry into the table. It takes three parameter. The first one is the processor name (
DELETE FROM CAMEL_MESSAGEPROCESSED WHERE processorName = ? AND messageId = ?
The statement which is used to delete the entry from the database. It takes two parameter. This first one is the processor name (
org.apache.camel.processor.idempotent.jdbc.JdbcMessageIdRepository could look like:
Using the JDBC based aggregation repository
Available as of Camel 2.6
JdbcAggregationRepository is an
AggregationRepository which on the fly persists the aggregated messages. This ensures that you will not loose messages, as the default aggregator will use an in memory only
JdbcAggregationRepository allows together with Camel to provide persistent support for the Aggregator.
It has the following options:
Mandatory: The name of the repository.
Whether the get operation should return the old existing Exchange if any existed. By default this option is
Whether or not recovery is enabled. This option is by default
If recovery is enabled then a background task is run every x'th time to scan for failed exchanges to recover and resubmit. By default this interval is 5000 millis.
Allows you to limit the maximum number of redelivery attempts for a recovered exchange. If enabled then the Exchange will be moved to the dead letter channel if all redelivery attempts failed. By default this option is disabled. If this option is used then the
An endpoint uri for a Dead Letter Channel where exhausted recovered Exchanges will be moved. If this option is used then the
Camel 2.11: Whether to store the message body as String which is human readable. By default this option is
Camel 2.11: Allows to store headers as String which is human readable. By default this option is disabled, storing the headers in binary format.
Camel 2.12: To turn on optimistic locking, which often would be needed in clustered environments where multiple Camel applications shared the same JDBC based aggregation repository.
Camel 2.12: Allows to plugin a custom
What is preserved when persisting
JdbcAggregationRepository will only preserve any
Serializable compatible data types. If a data type is not such a type its dropped and a
WARN is logged. And it only persists the
Message body and the
Message headers. The
Exchange properties are not persisted.
From Camel 2.11 onwards you can store the message body and select(ed) headers as String in separate columns.
JdbcAggregationRepository will by default recover any failed Exchange. It does this by having a background tasks that scans for failed Exchanges in the persistent store. You can use the
checkInterval option to set how often this task runs. The recovery works as transactional which ensures that Camel will try to recover and redeliver the failed Exchange. Any Exchange which was found to be recovered will be restored from the persistent store and resubmitted and send out again.
The following headers is set when an Exchange is being recovered/redelivered:
Is set to true to indicate the Exchange is being redelivered.
The redelivery attempt, starting from 1.
Only when an Exchange has been successfully processed it will be marked as complete which happens when the
confirm method is invoked on the
AggregationRepository. This means if the same Exchange fails again it will be kept retried until it success.
You can use option
maximumRedeliveries to limit the maximum number of redelivery attempts for a given recovered Exchange. You must also set the
deadLetterUri option so Camel knows where to send the Exchange when the
maximumRedeliveries was hit.
You can see some examples in the unit tests of camel-sql, for example this test.
To be operational, each aggregator uses two table: the aggregation and completed one. By convention the completed has the same name as the aggregation one suffixed with
"_COMPLETED". The name must be configured in the Spring bean with the
RepositoryName property. In the following example aggregation will be used.
The table structure definition of both table are identical: in both case a String value is used as key (id) whereas a Blob contains the exchange serialized in byte array.
However one difference should be remembered: the id field does not have the same content depending on the table.
In the aggregation table id holds the correlation Id used by the component to aggregate the messages. In the completed table, id holds the id of the exchange stored in corresponding the blob field.
Here is the SQL query used to create the tables, just replace
"aggregation" with your aggregator repository name.
Storing body and headers as text
Available as of Camel 2.11
You can configure the
JdbcAggregationRepository to store message body and select(ed) headers as String in separate columns. For example to store the body, and the following two headers
accountName use the following SQL:
And then configure the repository to enable this behavior as shown below:
Since they can contain any type of payload, Exchanges are not serializable by design. It is converted into a byte array to be stored in a database BLOB field. All those conversions are handled by the
JdbcCodec class. One detail of the code requires your attention: the
ClassLoadingAwareObjectInputStream has been reused from the Apache ActiveMQ project. It wraps an
ObjectInputStream and use it with the
ContextClassLoader rather than the
currentThread one. The benefit is to be able to load classes exposed by other bundles. This allows the exchange body and headers to have custom types object references.
PlatformTransactionManager is required to orchestrate transaction.
start method verify the connection of the database and the presence of the required tables. If anything is wrong it will fail during starting.
Depending on the targeted environment, the aggregator might need some configuration. As you already know, each aggregator should have its own repository (with the corresponding pair of table created in the database) and a data source. If the default lobHandler is not adapted to your database system, it can be injected with the
Here is the declaration for Oracle:
From Camel 2.12 onwards you can turn on
optimisticLocking and use this JDBC based aggregation repository in a clustered environment where multiple Camel applications shared the same database for the aggregation repository. If there is a race condition there JDBC driver will throw a vendor specific exception which the
JdbcAggregationRepository can react upon. To know which caused exceptions from the JDBC driver is regarded as an optimistick locking error we need a mapper to do this. Therefore there is a
org.apache.camel.processor.aggregate.jdbc.JdbcOptimisticLockingExceptionMapper allows you to implement your custom logic if needed. There is a default implementation
org.apache.camel.processor.aggregate.jdbc.DefaultJdbcOptimisticLockingExceptionMapper which works as follows:
The following check is done:
- If the caused exception is an
SQLExceptionthen the SQLState is checked if starts with 23.
- If the caused exception is a
- If the caused exception class name has "ConstraintViolation" in its name.
- optional checking for FQN class name matches if any class names has been configured
You can in addition add FQN classnames, and if any of the caused exception (or any nested) equals any of the FQN class names, then its an optimistick locking error.
Here is an example, where we define 2 extra FQN class names from the JDBC vendor.