How to reuse parts of the code within the same code?
In codes, it is possible to call a string, passing variables to it and all subsequent strings. This is also another method of creating variables and assigning them initial values.
For example, let's compare 2 values taken by one select:
=: if(condition: $sum{var: "num" = 1} = $sum{var: "num" = 2}; then: true; else: false)
sum: listSum(list: $select)
select: selectList(table: 'table'; field: 'field'; where: 'num' = $#num)
This code in condition calls the same select twice, but passes different variable values to it, and as a result, this is equivalent to:
=: if(condition: $sum_1 = $sum_2; then: true; else: false)
sum_1: listSum(list: $select_1)
select_1: select(table: 'table'; field: 'field'; where: 'num' = 1)
sum_2: listSum(list: $select_2)
select_2: select(table: 'table'; field: 'field'; where: 'num' = 2)
In such a small example, it is better not to use {} as they are harder to read, but if the reusable part is large, this significantly simplifies the code.
What is exec?
The exec function allows executing code contained in another field or passed in the code parameter as text.
When is exec effective?
If you have multiple fields executing the same code with different parameters. For example, we have an annual report where each field represents a month.
In the first field, we write:
=: listSum(list: $list)
list: selectList(table: 'table'; field: 'sum'; where: 'date' >= $datestart; where: 'date' <= $dateend)
datestart: var(name: "datestart"; default: "2021-01-01")
dateend: var(name: "dateend"; default: "2021-01-31")
Note that we take datestart and dateend through var here, because in the first field these variables will not be defined and we need default values.
In February, we write:
=: exec(code: "name_first_field"; var: "datestart" = "2021-02-01"; var: "dateend" = "2021-02-28")
Can we pass one var instead of several? Yes, we can:
=: exec(code: "name_first_field"; var: "dates" = $row)
row: rowCreate(field: "datestart" = "2021-02-01"; field: "dateend" = "2021-02-28")
But then we need to modify the code in the first column:
=: listSum(list: $list)
list: selectList(table: 'table'; field: 'sum'; where: 'date' >= $dates[datestart]; where: 'date' <= $dates[dateend])
~datestart: var(name: "dates"; default: $row)
row: rowCreate(field: "datestart" = "2021-01-01"; field: "dateend" = "2021-01-31")
If we run exec from the format section, how will it be executed?
exec executes code of the type from which it is called.
Will exec be executed if one of the parameters is not passed?
No, it won't. That's why we used default.
Another option, if in some cases the parameter is needed and in some cases it is not, is to pass it as an empty "" where it is not needed.
How can I store exec codes?
A good practice is to have a hidden field in the table where the executable code for exec will be stored in the corresponding section.
However, you can create a special table to store such extracted codes — but it is better to avoid this.