Row Value Expressions

Row Value Expressions that uses the Groovy syntax

Type: GROOVY

Just use ${ expression } or $->{ expression } in the configuration to identify the row expressions. The content of row expressions uses Groovy syntax, and all operations supported by Groovy are supported by row expressions. ${begin..end} denotes the range interval, ${[unit1, unit2, unit_x]} denotes the enumeration value. If there are multiple ${ expression } or $->{ expression } expressions in a row expression, the final result of the whole expression will be a Cartesian combination based on the result of each sub-expression.

Example:

• <GROOVY>t_order_${1..3} will be converted to t_order_1, t_order_2, t_order_3
• <GROOVY>${['online', 'offline']}_table${1..3} will be converted to online_table1, online_table2, online_table3, offline_table1, offline_table2, offline_table3

Row Value Expressions that uses a standard list

The LITERAL implementation will not convert any symbols to the expression part, and will directly obtain the output of the standard list from the input of the standard list. This helps address the issue that Groovy expressions are inconvenient to use under GraalVM Native Image.

Type: LITERAL

Example:

• <LITERAL>t_order_1, t_order_2, t_order_3 will be converted to t_order_1, t_order_2, t_order_3
• <LITERAL>t_order_${1..3} will be converted to t_order_${1..3}

Row Value Expressions that uses the Groovy syntax based on GraalVM Truffle’s Espresso implementation

This is an optional implementation, and you need to actively declare the following dependencies in the pom.xml of your own project. And make sure your own project is compiled with GraalVM CE 23.0.1 For JDK17.

<dependencies>
    <dependency>
        <groupId>org.apache.shardingsphere</groupId>
        <artifactId>shardingsphere-infra-expr-espresso</artifactId>
        <version>${shardingsphere.version}</version>
    </dependency>
</dependencies>

The user must install the Espresso component via GraalVM Updater, i.e. execute the following command in bash

gu install espresso

ESPRESSO is still an experimental module that allows the use of Row Value Expressions with Groovy syntax under GraalVM Native Image through the Espresso implementation of GraalVM Truffle.

The syntax part is the same as the GROOVY implementation rules.

Type: ESPRESSO

Example:

• <ESPRESSO>t_order_${1..3} will be converted to t_order_1, t_order_2, t_order_3
• <ESPRESSO>${['online', 'offline']}_table${1..3} will be converted to online_table1, online_table2, online_table3, offline_table1, offline_table2, offline_table3

Procedure

When using attributes that require the use of Row Value Expressions, such as in the data sharding feature, it is sufficient to indicate the Type Name of the specific SPI implementation under the actualDataNodes attribute.

If the Row Value Expressions does not indicate the Type Name of the SPI, the SPI implementation of GROOVY will be used by default.

Sample

rules:
- !SHARDING
  tables:
    t_order: 
      actualDataNodes: <LITERAL>ds_0.t_order_0, ds_0.t_order_1, ds_1.t_order_0, ds_1.t_order_1
      tableStrategy: 
        standard:
          shardingColumn: order_id
          shardingAlgorithmName: t_order_inline
      keyGenerateStrategy:
        column: order_id
        keyGeneratorName: snowflake
  defaultDatabaseStrategy:
    standard:
      shardingColumn: user_id
      shardingAlgorithmName: database_inline
  shardingAlgorithms:
    database_inline:
      type: INLINE
      props:
        algorithm-expression: <GROOVY>ds_${user_id % 2}
    t_order_inline:
      type: INLINE
      props:
        algorithm-expression: t_order_${order_id % 2}
  keyGenerators:
    snowflake:
      type: SNOWFLAKE

Related References

• Core Concept
• Data Sharding