EVD and Data Types
‘EVD’ stands for ‘EVL Data Definition’ and it is the way how to specify structure of data sets in EVL. It can be used either inline, as a component option, or in the *.evd file.
EVL uses mostly standard C++ data types, so most of them are well known.
EVD Structure
Firstly an example of evd file, which defines data types for some csv file:
id int sep=";" name string sep=";" null="" birth_date date sep=";" null="1970-01-01" amount decimal(12,3) sep=";" thousands_sep="," created_at datetime sep="\n" null="0000-00-00 00:00:00"
In general each nonempty line of EVD file looks like this:
<indent> Field_Name <blank> Data_Type <blank> EVD_Options |
where
- ‘<indent>’
might be empty, two spaces, 4 spaces, 6 spaces, etc., to define a substructure of compound data types, see Compound Types for details,
- ‘Field_Name’
TBA
- ‘Data_Type’
is one of:
-
string, see String -
char,uchar,short,ushort,int,uint,long,ulong,int128,uint128, see Integral Types -
decimal, see Decimal -
float,double, see Float and Double -
date,time,interval,datetime,timestamp, see Date and Time
-
- ‘EVD_Options’
is
<blank>separated list of options, see EVD Options- ‘<blank>’
is one or more spaces and/or tabs.
Comments
Standard C-style comments can be used in evd file, for example:
street_id int street_name string street_code string null="" // but NOT NULL in DB /* COMBAK: street_code will be replaced by street_num later this year street_num long */
Inline EVD
For the most of the EVL Components an inline EVD can be specified as an option. In such case comments are not allowed and the format is simply the same as for EVD in a file, just instead of newlines, commas are used to separate each field definition.
The same structure, as in above EVD Example, but as a component option (a comma separated list of fields with data types and options):
--data-definition='id int sep=";",
name string sep=";" null="",
birth_date date sep=";" null="1970-01-01",
amount decimal(12,3) sep=";" thousands_sep=",",
created_at datetime sep="\n" null="0000-00-00 00:00:00"'
Variables in EVD
There could be shell variables to be resolved in the evd file. For example:
$COMMON_EVD specific_field1 string null="" specific_field2 date null=""
will resolve the $COMMON_EVD environment variable and use such EVD. So having defined
export COMMON_EVD="$(cat common.evd)"
where common.evd might look like this:
id int valid_from datetime valid_to datetime
will resolve finally used EVD would be:
id int valid_from datetime valid_to datetime specific_field1 string null="" specific_field2 date null=""
In some situations, like having a dollar character as part of field name, this functionality may be switched off by setting
export EVL_ENVSUBST_EVD=0
in your job or in the shell.