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Support for nested database fields #158

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javierluraschi opened this issue Sep 11, 2018 · 2 comments

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@javierluraschi
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@javierluraschi javierluraschi commented Sep 11, 2018

It is increasingly common for databases to support unstructured data, for instance, in Apache Spark or Apache Drill; however, to my knowledge this might not be supported in dbplyr, is it?

A common case is to selected nested fields from within a field, two examples:

writeLines('[{"a":1,"b":{"a":10,"b":100}},{"a":2,"b":{"a":20,"b":200}}]', "test.json")

library(sparklyr)
sc <- spark_connect(master = "local")

nested_tbl <- spark_read_json(sc, "nested", "test.json")

# SQL query is supported
DBI::dbGetQuery(sc, "SELECT b.a FROM nested")
   a
1 10
2 20
# Query in dplyr...
nested_tbl %>% select(b.a)
 Error in .f(.x[[i]], ...) : object 'b.a' not found 
@hadley

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@hadley hadley commented Jan 2, 2019

I think we could add support for something like this:

nested_tbl %>% mutate(a = b$a)

If you're interested in this feature, the most helpful think would be to provide a bulleted for each database linking to the docs for nested fields

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@hadley hadley commented Jan 3, 2019

I think that's enough to suggest that we can translate $ to ..

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