使用 R 中的 DBI 包附加到 SQL Server 数据库时，字符列被转换为数字

Question

I have a database hosted using Microsoft SQL Server. It has a table project with columns project_id ( int identity ), project_code ( nvarchar not null ), and api_form ( nvarchar ). I have connected to this using the DBI package in R and ran the following code.

dbAppendTable(conn, 'project', data.frame(
  project_code = c("ABC123", "DEF456"),
  api_form = c(NA, NA)
))

When I query the entire table however, I get the following output.

project_id  project_code    api_form
1   1   NULL
2   2   NULL

I am not sure why the characters are now integers. Is there a way to add character data directly to the table or, if this is expected behaviour, how do I query the table to find the actually text I entered?

Answer 1

Classic overlook of data.frame() call that casts strings as factors by default. Your project_code renders as factor (ie, numeric columns with label values) and not characters. To resolve, simply pass stringsAsFactors=FALSE , so actual character values are appended to database table:

dbAppendTable(conn, 'project', 
              data.frame(
                 project_code = c("ABC123", "DEF456"),
                 api_form = c(NA, NA),
                 stringsAsFactors=FALSE 
              )
)

Alternatively, set the argument as global option for all data.frame() calls in your R session:

options(stringsAsFactors = FALSE)

dbAppendTable(conn, 'project', 
              data.frame(
                 project_code = c("ABC123", "DEF456"),
                 api_form = c(NA, NA) 
              )
)