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Data Transmission Service:Configure ETL in a data migration or synchronization task

最終更新日:Oct 24, 2024

Data Transmission Service (DTS) provides the extract, transform, and load (ETL) feature to help you process streaming data in real time. In combination with the efficient data replication capabilities of DTS, ETL can be used to extract, transform, process, and load streaming data. This topic describes how to configure ETL in a DTS task. You can use the ETL feature to filter data, mask data, record the modification time of data, and audit data modifications.

Background information

DTS is used for data migration and real-time data transmission between data sources. In some cases, you may need to transform or filter real-time data before the data is written to a database. To meet such requirements, DTS provides the ETL feature and allows you to use domain-specific language (DSL) statements to process data in a flexible manner. For more information about DSL, see the Overview of DSL section of this topic.

You can configure ETL by using one of the following methods:

Note

You can configure ETL in both data migration and data synchronization tasks. In this example, ETL is configured in a data synchronization task. You can also follow the procedure to configure ETL in a data migration task.

Supported database services

The following table describes the source and destination databases that are supported by the ETL feature.

Source database

Destination database

SQL Server

  • AnalyticDB for MySQL V3.0

  • SQL Server

  • MySQL

  • PolarDB for MySQL

MySQL

  • AnalyticDB for MySQL V3.0

  • AnalyticDB for PostgreSQL

  • Kafka

  • ClickHouse

  • MySQL

  • PolarDB for MySQL

  • Elasticsearch

Self-managed Oracle database

  • AnalyticDB for MySQL V3.0

  • AnalyticDB for PostgreSQL

  • Kafka

  • MaxCompute

  • PolarDB-X 2.0

  • PolarDB for PostgreSQL (Compatible with Oracle)

PolarDB for MySQL

  • AnalyticDB for MySQL V3.0

  • MySQL

  • PolarDB for MySQL

PolarDB for PostgreSQL (Compatible with Oracle)

  • AnalyticDB for MySQL V3.0

  • PolarDB for PostgreSQL (Compatible with Oracle)

PolarDB-X 1.0

  • Kafka

  • Tablestore

PolarDB-X 2.0

  • PolarDB-X 2.0

  • AnalyticDB for MySQL V3.0

  • MySQL

  • PolarDB for MySQL

Self-managed Db2 for LUW database

MySQL

Self-managed Db2 for i database

MySQL

PolarDB for PostgreSQL

  • PolarDB for PostgreSQL

  • PostgreSQL

PostgreSQL

  • PolarDB for PostgreSQL

  • PostgreSQL

TiDB

  • PolarDB for MySQL

  • MySQL

  • AnalyticDB for MySQL V3.0

MongoDB

Lindorm

Configure ETL when you create a data synchronization task

Usage notes

If the ETL script that you configure contains the operation to add a column, you must manually add a column to the destination table. Otherwise, the ETL script does not take effect. For example, if you configure the ETL script script:e_set(`new_column`, dt_now()), you must manually add the new_column column to the destination table.

Procedure

  1. Create a data synchronization task. For more information, see Overview of data synchronization scenarios.

  2. In the Advanced Settings section of the Configure Objects and Advanced Settings step, set the Configure ETL parameter to Yes. In the code editor, enter data processing statements based on the DSL syntax.

    Note

    If you want to drop entries whose values of the id column are greater than 3 by using DSL, you can use the script:e_if(op_gt(`id`, 3), e_drop()) statement. In this statement, op_gt is an expression function used to determine whether an entry is greater than a specific value, and id is a variable. This way, entries whose values of the id column are greater than 3 are filtered out.

  3. Click Next: Save Task Settings and Precheck and complete the subsequent steps.

Modify the ETL configurations of an existing data synchronization task

You can modify the ETL configurations in the following scenarios:

  • If the Configure ETL parameter is set to No for an existing data synchronization task, you can set this parameter to Yes and enter DSL statements.

  • If the Configure ETL parameter is set to Yes for an existing data synchronization task, you can modify the existing DSL statements or set this parameter to No.

    Important

    Before you modify the existing DSL statements, you must move the objects to be synchronized from the Selected Objects section to the Source Objects section and then add these objects to the Selected Objects section again.

Usage notes

  • For an existing data synchronization task, you cannot modify the destination table schema by modifying the ETL configurations of the task. You can modify the destination table schema only before the data synchronization task is started.

  • If you modify the ETL configurations, the data synchronization task may be interrupted. Proceed with caution.

  • The modification of the ETL configurations takes effect only on the incremental data generated after the modification.

  • The fields that are configured in the DSL script cannot be the fields that are filtered out by filter conditions. Otherwise, the task becomes abnormal.

  • The DSL script is case-sensitive. The names of the databases, tables, and fields that are configured in the DSL script must be the same as those in the source database.

  • The DSL script cannot contain multi-line expressions. You can use the e_compose function to combine multiple expressions into one expression.

Procedure

  1. Go to the Data Synchronization page of the new DTS console.

  2. Find the data synchronization whose ETL configurations you want to modify, click the 点点点 icon in the Actions column, and then click Modify ETL Configurations.

  3. In the Advanced Settings section of the Configure Objects and Advanced Settings step, set the Configure ETL parameter to Yes. In the code editor, enter data processing statements based on the DSL syntax.

    Note

    If you want to drop entries whose values of the id column are greater than 3 by using DSL, you can use the script:e_if(op_gt(`id`, 3), e_drop()) statement. In this statement, op_gt is an expression function used to determine whether an entry is greater than a specific value, and id is a variable. This way, entries whose values of the id column are greater than 3 are filtered out.

  4. Click Next: Precheck and Start Task and complete the subsequent steps.

Overview of DSL

DSL is a scripting language that is designed to process data in data synchronization scenarios. You can use conditional functions to process data of the string, date, and numeric types. DSL boasts the following characteristics that help you process data in a flexible manner:

  • Various functions: DSL provides a variety of functions and supports combined functions.

  • Simple syntax: DSL is easy to use. For more information about how to use DSL to filter, transform, and mask data, see the Typical scenarios section of this topic.

  • High efficiency: DSL has a minimal effect on the data synchronization performance because DSL uses the code generation mechanism.

Note
  • In a DSL statement, the column name is enclosed in backticks (`) instead of single quotation marks (').

  • The syntax of DSL for DTS has something in common with the syntax of DSL for Simple Log Service. DSL supports JSON functions and does not support functions for event splitting. For more information about the syntax of DSL for Simple Log Service, see Syntax overview.

Typical scenarios

  • Filter data

    • Filter out data by a numeric column: If an entry whose value of the id column is greater than 10000, drop this entry so that it is not synchronized to the destination database. Example: e_if(op_gt(`id`, 10000), e_drop()).

    • Filter out data by a specific string: If an entry whose value of the name column contains "hangzhou", drop this entry so that it is not synchronized to the destination database. Example: e_if(str_contains(`name`, "hangzhou"), e_drop()).

    • Filter out data by date: If an entry whose timestamp of the order column is earlier than a specific point in time, drop this entry so that it is not synchronized to the destination database. Example: e_if(op_lt(`order_timestamp`, "2015-02-23 23:54:55"), e_drop()).

    • Filter out data by multiple conditions:

      • If an entry whose value of the id column is greater than 1000 and value of the name column contains "hangzhou", drop this entry so that it is not synchronized to the destination database. Example: e_if(op_and(str_contains(`name`, "hangzhou"), op_gt(`id`, 1000)), e_drop()).

      • If an entry whose value of the id column is greater than 1000 or value of the name column contains "hangzhou", drop this entry so that it is not synchronized to the destination database. Example: e_if(op_or(str_contains(`name`, "hangzhou"), op_gt(`id`, 1000)), e_drop()).

  • Mask data

    • Mask the last four digits of a mobile phone number with four asterisks (*). Example: e_set(`phone`, str_mask(`phone`, 7, 10, '*')).

  • Record the time when data is modified

    • Add a column to all tables: If the value of the __OPERATION__ variable is INSERT, UPDATE, or DELETE, a column named dts_sync_time whose value is the same as the __COMMIT_TIMESTAMP__ variable of logs is added to all tables in the source database.

      e_if(op_or(op_or(
              op_eq(__OPERATION__, __OP_INSERT__),
              op_eq(__OPERATION__, __OP_UPDATE__)),
              op_eq(__OPERATION__, __OP_DELETE__)),
          e_set(dts_sync_time, __COMMIT_TIMESTAMP__))
    • Add a column to a specific table: If the value of the __OPERATION__ variable is INSERT, UPDATE, or DELETE, a column named dts_sync_time whose value is the same as the __COMMIT_TIMESTAMP__ variable of logs is added to the dts_test_table table in the source database.

      e_if(op_and(
            op_eq(__TB__,'dts_test_table'),
            op_or(op_or(
              op_eq(__OPERATION__,__OP_INSERT__),
              op_eq(__OPERATION__,__OP_UPDATE__)),
              op_eq(__OPERATION__,__OP_DELETE__))),
            e_set(dts_sync_time,__COMMIT_TIMESTAMP__))
      Note

      To perform the preceding operations, you must add the dts_sync_time column to the corresponding tables in the destination database before the data synchronization task is started.

  • Audit data modifications

    • Record the type and time of the data modifications in tables: 1. Record the data modification type in the operation_type column of the destination database. 2. Record the time when data is modified in the updated column of the destination database.

      e_compose(
          e_switch(
              op_eq(__OPERATION__,__OP_DELETE__), e_set(operation_type, 'DELETE'),
              op_eq(__OPERATION__,__OP_UPDATE__), e_set(operation_type, 'UPDATE'),
              op_eq(__OPERATION__,__OP_INSERT__), e_set(operation_type, 'INSERT')),
          e_set(updated, __COMMIT_TIMESTAMP__),
          e_set(__OPERATION__,__OP_INSERT__)
      )
      Note

      You must add the operation_type and updated columns to the tables in the destination database before the data synchronization task is started.

DSL syntax

Constants and variables

  • Constants

    Data type

    Example

    int

    123

    float

    123.4

    string

    "hello1_world"

    boolean

    true or false

    datetime

    DATETIME('2021-01-01 10:10:01')

  • Variables

    Variable

    Description

    Data type

    Example

    __TB__

    The table name.

    string

    table

    __DB__

    The database name.

    string

    mydb

    __OPERATION__

    The operation type.

    string

    __OP_INSERT__,__OP_UPDATE__,__OP_DELETE__

    __BEFORE__

    The previous image value of the UPDATE operation, which is the column value before the UPDATE operation is performed.

    Note

    The DELETE operation has only the previous image value.

    N/A

    v(`column_name`,__BEFORE__)

    __AFTER__

    The new image value of the UPDATE operation, which is the column value after the UPDATE operation is performed.

    Note

    The INSERT operation has only the new image value.

    N/A

    v(`column_name`,__AFTER__)

    __COMMIT_TIMESTAMP__

    The time when the transaction was committed.

    datetime

    '2021-01-01 10:10:01'

    `column`

    The name of the column.

    string

    `id` or `name`

Expression functions

  • Arithmetic operations

    Operation

    Syntax

    Valid value

    Return value

    Example

    Addition

    op_sum(value1, value2)

    • value1: an integer or a floating-point number.

    • value2: an integer or a floating-point number.

    If value1 and value2 are integers, an integer is returned. Otherwise, a floating-point number is returned.

    op_sum(`col1`, 1.0)

    Subtraction

    op_sub(value1, value2)

    • value1: an integer or a floating-point number.

    • value2: an integer or a floating-point number.

    If value1 and value2 are integers, an integer is returned. Otherwise, a floating-point number is returned.

    op_sub(`col1`, 1.0)

    Multiplication

    op_mul(value1, value2)

    • value1: an integer or a floating-point number.

    • value2: an integer or a floating-point number.

    If value1 and value2 are integers, an integer is returned. Otherwise, a floating-point number is returned.

    op_mul(`col1`, 1.0)

    Division

    op_div_true(value1, value2)

    • value1: an integer or a floating-point number.

    • value2: an integer or a floating-point number.

    If value1 and value2 are integers, an integer is returned. Otherwise, a floating-point number is returned.

    op_div_true(`col1`, 2.0). In this example, if the value of col1 is 15, 7.5 is returned.

    Modulo

    op_mod(value1, value2)

    • value1: an integer or a floating-point number.

    • value2: an integer or a floating-point number.

    If value1 and value2 are integers, an integer is returned. Otherwise, a floating-point number is returned.

    op_mod(`col1`, 10). In this example, if the value of col1 is 23, 3 is returned.

  • Logical operations

    Operation

    Syntax

    Valid value

    Return value

    Example

    Equal to

    op_eq(value1, value2)

    • value1: an integer, a floating-point number, or a string.

    • value2: an integer, a floating-point number, or a string.

    true or false

    op_eq(`col1`, 23)

    Greater than

    op_gt(value1, value2)

    • value1: an integer, a floating-point number, or a string.

    • value2: an integer, a floating-point number, or a string.

    true or false

    op_gt(`col1`, 1.0)

    Less than

    op_lt(value1, value2)

    • value1: an integer, a floating-point number, or a string.

    • value2: an integer, a floating-point number, or a string.

    true or false

    op_lt(`col1`, 1.0)

    Greater than or equal to

    op_ge(value1, value2)

    • value1: an integer, a floating-point number, or a string.

    • value2: an integer, a floating-point number, or a string.

    true or false

    op_ge(`col1`, 1.0)

    Less than or equal to

    op_le(value1, value2)

    • value1: an integer, a floating-point number, or a string.

    • value2: an integer, a floating-point number, or a string.

    true or false

    op_le(`col1`, 1.0)

    AND

    op_and(value1, value2)

    • value1: a Boolean value.

    • value2: a Boolean value.

    true or false

    op_and(`is_male`, `is_student`)

    OR

    op_or(value1, value2)

    • value1: a Boolean value.

    • value2: a Boolean value.

    true or false

    op_or(`is_male`, `is_student`)

    IN

    op_in(value, json_array)

    • value: an arbitrary value.

    • json_array: a JSON string.

    true or false

    op_in(`id`,json_array('["0","1","2","3","4","5","6","7","8"]'))

    Determine whether the value is empty

    op_is_null(value)

    value: an arbitrary value.

    true or false

    op_is_null(`name`)

    Determine whether the value is not empty

    op_is_not_null(value)

    value: an arbitrary value.

    true or false

    op_is_not_null(`name`)

  • String functions

    Operation

    Syntax

    Valid value

    Return value

    Example

    Append strings

    op_add(str_1,str_2,...,str_n)

    • str_1: a string.

    • str_2: a string.

    • ...

    • str_n: a string.

    The string after the append operation.

    op_add(`col`,'hangzhou','dts')

    Format strings and append strings

    str_format(format, value1, value2, value3, ...)

    • format: a string. Braces ({}) are used as placeholders. Example: "part1: {}, part2: {}".

    • value1: an arbitrary value.

    • value2: an arbitrary value.

    The string after the format operation.

    str_format("part1: {}, part2: {}", `col1`, `col2`). In this example, if the value of col1 is ab and the value of col2 is 12, "part1: ab, part2: 12" is returned.

    Replace strings

    str_replace(original, oldStr, newStr, count)

    • original: the original string.

    • oldStr: the string to be replaced.

    • newStr: the string after the replacement.

    • count: an integer that indicates the maximum number of times that a string can be replaced. A value of -1 indicates that all oldStr is replaced with newStr.

    The string after the replace operation.

    Example 1: str_replace(`name`, "a", 'b', 1). In this example, if the name is aba, bba is returned. Example 2: str_replace(`name`, "a", 'b', -1). In this example, if the name is aba, bbb is returned.

    Replace strings in the values of fields of all string types, such as the VARCHAR, TEXT, or CHAR type

    tail_replace_string_field(search, replace, all)

    • search: the string to be replaced.

    • replace: the string after the replacement.

    • all: indicates whether to replace all matched strings. Only a value of true is supported.

      Note

      If you do not need to replace all matched strings, use the str_replace() function.

    The string after the replace operation.

    tail_replace_string_field('\u000f','',true). In this example, all "\u000f" strings in the field values of the string type are replaced with spaces.

    Remove specific characters at the start and end of a string

    str_strip(string_val, charSet)

    • string_val: the original string.

    • char_set: the set of the first characters and the last characters of the string.

    The string after the remove operation.

    str_strip(`name`, 'ab'). In this example, if the name is axbzb, xbz is returned.

    Convert strings to lowercase letters

    str_lower(value)

    value: a column of the string type or a string constant.

    The string after the convert operation.

    str_lower(`str_col`)

    Convert strings to uppercase letters

    str_upper(value)

    value: a column of the string type or a string constant.

    The string after the convert operation.

    str_upper(`str_col`)

    Convert strings to numbers

    cast_string_to_long(value)

    value: a string.

    The integer after the convert operation.

    cast_string_to_long(`col`)

    Convert numbers to strings

    cast_long_to_string(value)

    value: an integer.

    The string after the convert operation.

    cast_long_to_string(`col`)

    Count strings

    str_count(str,pattern)

    • str: a column of the string type or a string constant.

    • pattern: the substring to query.

    The number of times for which the substring appears.

    str_count(`str_col`, 'abc'). In this example, if the value of str_col is zabcyabcz, 2 is returned.

    Query strings

    str_find(str, pattern)

    • str: a column of the string type or a string constant.

    • pattern: the substring to query.

    The position in which the substring matches for the first time. If no match is found, -1 is returned.

    str_find(`str_col`, 'abc'). In this example, if the value of str_col is xabcy, 1 is returned.

    Determine whether a string contains only letters

    str_isalpha(str)

    str: a column of the string type or a string constant.

    true or false

    str_isalpha(`str_col`)

    Determine whether a string contains only digits

    str_isdigit(str)

    • str: a column of the string type or a string constant.

    true or false

    str_isdigit(`str_col`)

    Regular expression match

    regex_match(str,regex)

    • str: a column of the string type or a string constant.

    • regex: a regular expression.

    true or false

    regex_match(__TB__,'user_\\d+')

    Mask part of a string with specific characters. This operation can be used for data masking. For example, mask the last four digits of a mobile phone number with four asterisks (*).

    str_mask(str, start, end, maskStr)

    • str: a column of the string type or a string constant.

    • start: an integer that indicates the start position of the masking. The minimum value is 0.

    • end: an integer that indicates the end position of the masking. The maximum value is the length of the string minus 1.

    • maskStr: a string. The length is 1. Example: #.

    The string whose part from start to end is masked with the specified characters.

    str_mask(`phone`, 7, 10, '#')

    Truncate a string from the cond string to the last character

    substring_after(str, cond)

    • str: the original string.

    • cond: a string.

    The string after the truncate operation.

    Note

    The return value does not contain the cond string.

    substring_after(`col`, 'abc')

    Truncate a string from the first character to the cond string

    substring_before(str, cond)

    • str: the original string.

    • cond: a string.

    The string after the truncate operation.

    Note

    The return value does not contain the cond string.

    substring_before(`col`, 'efg')

    Truncate a string from the cond1 string to the cond2 string

    substring_between(str, cond1, cond2)

    • str: the original string.

    • cond1: a string.

    • cond2: a string.

    The string after the truncate operation.

    Note

    The return value does not contain the cond1 and cond2 strings.

    substring_between(`col`, 'abc','efg')

    Determine whether the value is of the string type

    is_string_value(value)

    value: a string or a column name.

    true or false

    is_string_value(`col1`)

    Replace strings in the field values of the string type. The replacement starts from the end of the field values.

    tail_replace_string_field(search, replace, all)

    search: the string to be replaced.

    replace: the string after the replacement.

    all: indicates whether to replace all matched strings. Valid values: true and false.

    The string after the replace operation.

    In the following example, all "\u000f" strings in the field values of the string type are replaced with spaces:

    tail_replace_string_field('\u000f','',true)

    Query the value of a field in a MongoDB document

    bson_value("field1","field2","field3", ...)

    • field1: the name of the level -1 field.

    • field2: the name of the level -2 field.

    The value of the corresponding field in the document.

    • e_set(`user_id`, bson_value("id"))

    • e_set(`user_name`, bson_value("person","name"))

  • Time functions

    Operation

    Syntax

    Valid value

    Return value

    Example

    Query the current time

    dt_now()

    N/A

    A value of the DATETIME data type that is accurate to seconds.

    dts_now()

    dt_now_millis()

    N/A

    A value of the DATETIME data type that is accurate to milliseconds.

    dt_now_millis()

    Convert a UTC timestamp in seconds to a DATETIME value

    dt_fromtimestamp(value,[timezone])

    • value: an integer.

    • timezone: the time zone. This parameter is optional.

    A value of the DATETIME data type that is accurate to seconds.

    dt_fromtimestamp(1626837629)

    dt_fromtimestamp(1626837629,'GMT+08')

    Convert a UTC timestamp in milliseconds to a DATETIME value

    dt_fromtimestamp_millis(value,[timezone])

    • value: an integer.

    • timezone: the time zone. This parameter is optional.

    A value of the DATETIME data type that is accurate to milliseconds.

    dt_fromtimestamp_millis(1626837629123);

    dt_fromtimestamp_millis(1626837629123,'GMT+08')

    Convert a DATETIME value to a UTC timestamp in seconds

    dt_parsetimestamp(value,[timezone])

    • value: a value of the DATETIME data type.

    • timezone: the time zone. This parameter is optional.

    The integer after the convert operation.

    dt_parsetimestamp(`datetime_col`)

    dt_parsetimestamp(`datetime_col`,'GMT+08')

    Convert a DATETIME value to a UTC timestamp in milliseconds

    dt_parsetimestamp_millis(value,[timezone])

    • value: a value of the DATETIME data type.

    • timezone: the time zone. This parameter is optional.

    The integer after the convert operation.

    dt_parsetimestamp_millis(`datetime_col`)

    dt_parsetimestamp_millis(`datetime_col`,'GMT+08')

    Convert a DATETIME value to a string

    dt_str(value, format)

    • value: a value of the DATETIME data type.

    • format: a string that indicates the time format. Example: yyyy-MM-dd HH:mm:ss.

    The string after the convert operation.

    dt_str(`col1`, 'yyyy-MM-dd HH:mm:ss')

    Convert a string to a DATETIME value

    dt_strptime(value,format)

    • value: a string.

    • format: a string that indicates the time format. Example: yyyy-MM-dd HH:mm:ss.

    The DATETIME value after the convert operation.

    dt_strptime('2021-07-21 03:20:29', 'yyyy-MM-dd hh:mm:ss')

    Change the time by increasing or decreasing the values of one or more time granularities, such as year, month, day, hour, minute, and second

    dt_add(value, [years=intVal],

    [months=intVal],

    [days=intVal],

    [hours=intVal],

    [minutes=intVal]

    )

    • value: a value of the DATETIME data type.

    • intVal: an integer.

      Note

      A minus sign (-) indicates that the value of the specified time granularity is decreased.

    The DATETIME value after the change operation.

    • dt_add(datetime_col,years=-1)

    • dt_add(datetime_col,years=1,months=1)

  • Conditional expression

    Operation

    Syntax

    Valid value

    Return value

    Example

    Return a value based on the result of the condition. This expression is similar to the ternary operator (? :) in the C language.

    (cond ? val_1 : val_2)

    • cond: a field or an expression whose value is a Boolean value.

    • val_1: return value 1.

    • val_2: return value 2.

      Note

      The values of val_1 and val_2 must be of the same data type.

    If the value of cond is true, val_1 is returned. Otherwise, val_2 is returned.

    (id>1000? 1 : 0)

Global functions

  • Flow control functions

    Operation

    Syntax

    Description

    Example

    IF statement

    e_if(bool_expr, func_invoke)

    • bool_expr: a Boolean constant or a function. A Boolean constant: true or false. A function: op_gt(`id`, 10).

    • func_invoke: a function. e_drop,e_keep,e_set,e_if,e_compose

    e_if(op_gt(`id`, 10), e_drop()). In this example, if an entry whose value of the id column is greater than 10, this entry is dropped.

    IF ELSE statement

    e_if_else(bool_expr, func_invoke1, func_invoke2)

    • bool_expr: a Boolean constant or a function. A Boolean constant: true or false. A function: op_gt(`id`, 10).

    • func_invoke1: a function. Invoke this function if the condition is true.

    • func_invoke2: a function. Invoke this function if the condition is false.

    e_if_else(op_gt(`id`, 10), e_set(`tag`, 'large'), e_set(`tag`, 'small')). In this example, if an entry whose value of the id column is greater than 10, the tag column is set to large. Otherwise, the tag column is set to small.

    SWITCH statement that contains multiple conditions and a default operation

    s_switch(condition1, func1, condition2, func2, ..., default = default_func)

    • condition1: a Boolean constant or a function. A Boolean constant: true or false. A function: op_gt(`id`, 10).

    • func_invoke: a function. If condition1 is true, invoke this function and finish the statement. Otherwise, proceed to the next condition.

    • default_func: a function. If the preceding conditions are false, invoke this function.

    e_switch(op_gt(`id`, 100), e_set(`str_col`, '>100'), op_gt(`id`, 90), e_set(`str_col`, '>90'), default=e_set(`str_col`, '<=90'))

    Combination of multiple operations

    e_compose(func1, func2, func3, ...)

    • func1: a function. Valid values: e_set, e_drop, and e_if.

    • func2: a function. Valid values: e_set, e_drop, and e_if.

    e_compose(e_set(`str_col`, 'test'), e_set(`dt_col`, dt_now())). In this example, the value of the str_col column is set to test, and the value of the dt_col column is set to the current time.

  • Data manipulation functions

    Operation

    Syntax

    Description

    Example

    Drop an entry so that it is not synchronized to the destination database

    e_drop()

    N/A

    e_if(op_gt(`id`, 10), e_drop()). In this example, entries whose values of the id column are greater than 10 are dropped.

    Retain an entry so that it is synchronized to the destination database

    e_keep(condition)

    condition: a Boolean expression.

    e_keep(op_gt(id, 1)). In this example, only entries whose values of the id column are greater than 1 are synchronized.

    Specify the value of a column

    e_set(`col`, val)

    • col: the name of the column.

    • val: a constant or a function. The data type of the value of val must match that of col.

    • e_set(`dt_col`, dt_now()). In this example, the value of the dt_col column is set to the current time.

    • e_set(`col1`, `col2` + 1). In this example, the value of the col1 column is set to the value of the col2 column plus 1.

    Retain fields, drop fields, and use the field name mapping feature during data migration or synchronization between MongoDB databases

    e_expand_bson_value('*', 'fieldA', {"fieldB":"fieldC"})

    • *: the name of the field to be retained. * indicates all fields.

    • fieldA: the name of the field to be dropped.

    • {"fieldB":"fieldC"}: the field name mapping. fieldB indicates the name of the field in the source database, and fieldC indicates the name of the field in the destination database.

      Note

      The field name mapping is an optional expression.

    e_expand_bson_value("*", "_id,name"). In this example, the fields other than _id and name are written to the destination database.