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TheDatabaseJoinertransformer is similar to theFeatureJoinerorFeatureMerger,but instead of merging two streams of features and an in-memory join,it merges one stream of features with data read from an external database.
Still trying to decide which is the most appropriate join transformer to use?See the article Merging or Joining Spreadsheet or Database Data
For example,a dataset of AddressPoints has an AddressId number,but no postal address.The DatabaseJoiner transformer is being used to join data from an address table onto the AddressPoints data.In this case the address point features are obtaining address data directly from an address table in a PostGIS database.
The parameters dialog for the DatabaseJoiner looks like this:
Again,AddressId is being used as the join key.
Incoming features (AddressPoints) that do not find a match in the join table (PostalAddress) are output via the Unjoined port and also have the attribute _matched_records = 0
Example workspace with DatabaseJoiner.
TheDatabaseJoinerhas a number of advantages over other data joining transformers such as the FeatureMerger:
The articleJoin CSV Data to a Database Table with the DatabaseJoinermatches CSV crime data to a database table of road information,so that we can determine which roads show the most crime activity.
The articleBuild Major Roads from GPS Pointstakes a set of GPS points and converts them into line work showing a road network.The attributes relating to the roads is held in an Access database.These attributes are joined to the GPS line work using the DatabaseJoiner,adding value to the output.
Performing spatial queries on database tables using the FeatureReader
Join CSV File to a Database Table with the DatabaseJoiner
Merging or Joining Spreadsheet or Database Data
Converting to PostGIS: Write to an Existing Table
Let the Database Do the Work: Reading
Working with Foreign Keys: Writing Database Tables
Viewing and Inspecting PostGIS Data
Combining Multiple Streams of Data (Append vs.Merge or Join)
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