This is the first post in the series of posts covering the Open Source projects I am working on.

That post in particular covers dynocsv, which allows exporting DynamoDB table into the CSV file, either the whole table or part of it by query with hash/sort keys, both on table or index.

NAME:
   dynocsv - Export DynamoDB table into CSV file

USAGE:
   dynocsv     
        --table/-t                                     <table> 
        [--columns/-c                                  <comma separated columns>] 
        [--skip-columns/-sc                            <comma separated columns to skip>] 
        [--limit/-l                                    <number>]
        [--profile/-p                                  <AWS profile>]
        [--index/-i                                    <index to query instead of table>]
        [--hash                                        <hash value>]
        [--sort                                        <sort value>]
        [--sort-[gt, ge, lt, le, begins-with, between] <sort value>]
        [--output/-o                                   <output file name>]

VERSION:
   1.1.3

AUTHOR:
   (c) Aliaksandr Kazlou

COMMANDS:
     help, h  Shows a list of commands or help for one command

GLOBAL OPTIONS:
   --table value, -t value           table to export
   --index value, -i value           index to query if hash/sort are set instead of table (which is default)
   --columns value, -c value         columns to export from the table, if omitted, all columns will be exported (muttaly exclusive with "skip-columns")
   --skip-columns value, --sc value  columns skipped from export from the table, if omitted, all columns will be exported (muttaly exclusive with "columns")
   --limit value, -l value           limit number of records returned, if not set (i.e. 0) all items are fetched (default: 0)
   --profile value, -p value         AWS profile to use to connect to DynamoDB, otherwise the value from AWS_PROFILE env var is used if available, or then "default" if it is not set or empty
   --hash value                      Limit query by hash value (eq/=)
   --sort value                      Limit query by sort value (eq/=)
   --sort-gt value                   Limit query by sort value (gt/>)
   --sort-ge value                   Limit query by sort value (ge/>=)
   --sort-lt value                   Limit query by sort value (lt/<)
   --sort-le value                   Limit query by sort value (le/<=)
   --sort-begins-with value          Limit query by sort value (begins with)
   --sort-between value              Limit query by sort value (between), values are separated by comma, i.e. "value1,value2"
   --output value, -o value          output file, or the default <table name>.csv will be used
   --help, -h                        show help
   --version, -v                     print the version

Installation

Use the go command:

$ go get github.com/zshamrock/dynocsv

Or using snap:

$ snap install dynocsv

snap connect dynocsv:aws-config-credentials

otherwise, it fails to read the credentials and will fail with

2019/10/24 17:34:14 MissingRegion: could not find region configuration panic: MissingRegion: could not find region configuration

AWS Connection

Connection to the AWS is established using profile credentials. There are 2 options to provide the AWS profile to use:

1. use explicit --profile/-p option to set the AWS profile to use, i.e. dynocsv -p <profile name> -t <table name>
2. set the env var $AWS_PROFILE before running the app, i.e. AWS_PROFILE=<profile name> dynocsv -t <table name>

If no explicit profile value is set, it looks for the env var $AWS_PROFILE if present or otherwise fallbacks to the default profile.

Query

By default Scan operation is run to fetch all the data.

If --hash and any of the --sort CLI arguments are provided, Query operation will be run to query the corresponding data based on the key conditions specified by --hash and --sort values.

The query can be run either on the table (default) or index (if --index argument is set).

CSV Headers

As DynamoDB is a column-based family of DBs, technically each row could have a different number of columns/attributes, with different names. And also DynamoDB only allows fetching the description about attributes that are part of table/index hash or sort keys. So, in that case, it might not be possible to resolve all the attribute names (and so CSV headers) until all the data is read first.

And potentially the data size could be big enough to not fit in memory or be not practical to keep all data in memory. So currently it keeps the first 1000 read records in memory in the assumption that all possible attributes will be seen up to that point. And so write the CSV headers accordingly.

If even after 1000 records the new attribute is detected the tool outputs at the end of export the headers line into stdout which you would need manually to replace with the existing CSV headers row.

Attributes Order

The attributes in the output CSV are sorted in the following order:

• if --index CLI argument has not been provided table hash/sort keys are coming first, then all available global secondary indexes' hash/sort keys (in alphabetical order by index names), and then all the rest of the attributes sorted alphabetically
• if --index CLI argument is set, the order will be the same as above with the exception that that index's hash/sort keys will come first before the table's hash/sort keys, then all the remaining other indexes' hash/sort keys, and the rest of the attributes sorted alphabetically

Limits

Currently, there are the following limitations:

• String, Boolean, Number, Map, StringSet, NumberSet and List data types are supported to export the data from, attributes with other data type (like binary) will still be present, but the value will be "" (empty string)
• there is no pause or proper throttling according to the current set table's RCU, so you might need manually to increase the RCU value temporarily for the period of running the export

The tool is free, easy to install and use. Please, give it a try, and see if it helps to solve your problem. Also feel free to create the feature request or report the bug Issue.

As well as Star or support on Patreon.