Is there a way to draw arrows from/to table rows in PlantUML? - uml

Question

If you had an ER-Diagram in PlantUML, stylized this way using tables, is there a way to connect the table rows with arrows?
#startuml
entity User {
<#transparent,#transparent>| <color:gold><&key> | <b>id |<r> bigint |
| | name |<r> varchar |
}
entity Email {
<#transparent,#transparent>| <color:gold><&key> | <b>id |<r> bigint |
| <color:purple><&link-intact> | <i>user_id |<r> bigint |
| | address |<r> varchar |
}
User::id -> Email::user_id
#enduml
I know you can get exactly what I want using fields, but the way it looks is a bit boring and simple.
Also, there is a bit of micromanagement by putting the tabs characters.
#startuml
entity User {
#id \t\t bigint
name \t varchar
}
entity Email {
#id \t\t bigint
+user_id \t bigint
address \t varchar
}
User::id -> Email::user_id
#enduml

Answer 1

There is a workaround that will not involve the tab micromanagement in the member/fields approach.
You can design a procedure, to take care of the tabs characters for you. The only thing left is to replace the member visibility icons (something I do not know how to do).
This approach requires the table data to be store as a JSON (one per each table).
For example:
table.iuml
#startuml
!global $tab_size = 4 ' The tab size in plantuml is 4 chars wide
' Returns the size in tabs, rounded down, that the $data has
!function $tab_size($data)
!return %strlen($data)/$tab_size
!endfunction
' Get the maximum number of tabs from the $data array
!function $get_max_tabs($data)
!local $tabs = 0
!foreach $field in $data
!local $field_tabs = $tab_size($field.name)
!if ($tabs < $field_tabs)
!local $tabs = $field_tabs
!endif
!endfor
!return $tabs
!endfunction
' Get the field name followed by the "perfect" number of tabs
!function $get_name($name, $max_tabs)
!local $tabs = "\t"
!local $length = $tab_size($name)
!while $max_tabs > $length
!local $tabs = $tabs + "\t"
!local $length = $length + 1
!endwhile
!return $name + $tabs
!endfunction
' Create a entity member for the table field
!procedure field($data, $max_tabs)
!local $field = $get_name($data.name, $max_tabs) + $data.type
!if %json_key_exists($data, "index")
!if $data.index == "primary"
# $field
!elseif $data.index == "unique"
~ $field
!elseif $data.index == "simple"
+ $field
!endif
!else
$field
!endif
!endprocedure
' Process the JSON data to create a plantuml entity
!procedure table($data)
!local $tabs = $get_max_tabs($data.fields)
entity $data.name {
!foreach $field in $data.fields
field($field, $tabs)
!endfor
}
!endprocedure
#enduml
database.puml
#startuml
!include table.iuml
!$user = %load_json("user.json")
table($user)
!$email = %load_json("email.json")
table($email)
user::id -> email::user_id
#enduml
user.json
{
"name": "user",
"fields": [
{
"name": "id",
"type": "bigint",
"index": "primary"
},
{
"name": "name",
"type": "varchar"
}
]
}
email.json
{
"name": "email",
"fields": [
{
"name": "id",
"type": "bigint",
"index": "primary"
},
{
"name": "user_id",
"type": "bigint"
},
{
"name": "address",
"type": "varchar"
}
]
}
Obtaining the following diagram