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1. Operations
   1. Perform single + batch read on single + multiple dataset from script transform
   2. Perform single + batch read on DistributedCache single + multiple files from script transform
2. Supported datasets tables for lookup
   Key
   1. KeyValueTable dataset
   2. ObjectMappedTable dataset
   3. CSV files treated as a list of key-value tablepairs
   4. ObjectMappedTable
3. Optional caching with time-based expiration

Design

1.  Lookup interface 

   Code Block
   interface Lookup<T> { T lookup(String key); Map<String, T> lookup(String... keys); Map<String, T> lookup(Set<String> keys); }

2. Implement Lookup in KeyValueTable and ObjectMappedTable
   1. KeyValueTable implements Lookup<String>
   2. ObjectMappedTable implements Lookup<StructuredRecord>
3. DatasetConfigurer changes
   1. Add method: void useDataset(String datasetName);
4. ScriptTransform changes

   1. Add configuration property for declaring lookup tables to use, properties for each table (e.g. dataset properties)

      Code Block
      "tables": [ { "name":"purchases", "type":"dataset", "properties": { "dataset":"purchases", "properties":{.. dataset properties ..}, "enableCache":"true", "cacheExpiry":1234 } }, {"name":"ip2geo", "type":"file", "properties":{"file":"/data/ip2geo.csv"}} ]

   2. configure(): verify tables (datasets and files) exist by calling DatasetConfigurer.useDataset()
   3. transform(): execute lookup methods in a transaction, provide Lookup instance to script

      1. Options for lookup usage: 

         Code Block
         var result = context.getLookup("purchases").lookup(user);

      2. Options for batch lookup usage:

         Code Block
         var result = context.getLookup("purchases").lookup(["alice", "bob"]); // do something with result["alice"] // do something with result["bob"]