Unlocking The Power Of Unconnected Lookup In Talend
Sometimes the lookups are so big that they don’t fit in memory and there is no better way to unload the data for heavy lookups and use it multiple times in the same and child jobs.
To overcome this issue BigData Dimension team has created components to support Unconnected Lookup functionality in Talend to be able to do lookups without using tMap or the tJoin components and get the flexibility of loading the data once and use it in multiple jobs. If the dataset doesn’t fit in memory we can select a disk based storage to store the data and also use that stored data in the child jobs.
This allows us to create and populate HashMaps. The append existing option is shared between the Basic and Advanced settings. When creating a new hash we have the option to select whether we want to store the data in-memory or on disk.
By default we use the keys defined in the schema. This can be overridden, by checking the „Manually Provide Key Column name” checkbox. When checked we can provide one ore more key columns. If the key is complex the columns can be listed using a comma separated list.
The values work the same way, we can define one ore more columns separated by comma.
!!! Keep in mind that you can’t use context or other dynamic variables here because these informations are required when the Java code is generated. !!!
These settings are used when the input schema type is Dynamic. The key and value fields work similarly to the ones in the Basic settings, but their value are evaluated during runtime, hence globalMap, context variables can be used here.
To be used with regular schemas. Basic mapping contains the 1:1 column mapping. Lookup mapping contains the lookups for the new columns.
The table column names are self explaining. Input Key can contain more columns separated by a comma. Value column needs to have a valid column name defined in the lookup. Join Mode: in case of INNER join, if the lookup fails the row is skipped. (Thrown out)
To be used with dynamic Schemas. Columns to be removed is a comma separated list of the columns that we’d like to remove from the dynamic line. Columns to lookup work similarly to the one in the Basic settings, but here we can’t define the new types in the schema, that needs to be defined here. Talend Type and Db Type is used for that.
Column calculations work the same way: we add a new column then populate its value. They input column can be added as: input_row.column_name which in runtime gets replaced with the actual value.
How to Use Examples
Basic Map usage
This section shows how can we use the map with predefined schemas.
We’re going to have 2 lookups and will do 1 + 2 + 1 lookup. The 2 lookups will look like this:
1.) EMP: Lookup 1
Lookup 1 Basic settings
2.) LOC: Lookup 2
Lookup 2 Basic Settings
3.) Job Overview
4.) Input: Main input
What we can do with this input is a lookup based onthe employee. We can look up the emp_name and emp_loc to this.
5.) Basic Settings
Upon running this yields the following:
We can do another lookup based on the employee_site column.
6.) Basic Settings
Which results in:
We can use multiple lookups and multiple value from a lookup. A lookup can be used as many times as required.
We can use different keys for the same lookup:
8.) Basic Settings – Lookup Mapping
Please note that we get the Object map from the lookup once then we can look it up as many times as required.
here we use the same map, but with different keys. We want to know the location name for both the sales location and employee base location. This requires 2 lookups.
Using Dynamic Schema
The main challenge is the modifying of the dynamic schema, talend is very sensitive to this, so it needs to be executed carefully else we’ll get different results than expected. Most of the functions around dynamic schema will soak the error silently, and has no feedback if it was executed successfully.
Using a lookup populated in a child job
In this case the parent jobs will look like:
11. Overall look
12. tRunJob setting
Use CTRL + SPACE to bring up the _DB aftervariable. lookup type is Object!
Then we place a single outputcomponent in all the child jobs where we want to use the parent:
13. Advanced Setting
No other parameters have to be added. Then use it like it was populated in that job.
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