Can't set different json values with different values - bash

Question

Linux Mint 20.2
Here report.empty.json
{
"total": 0,
"project": "",
"Severity": [],
"issues": []
}
I want to set value = 500 (int value) to "total" and "MY_PROJECT".
To do this I use tool "jq"
Here by bash script file:
#!/bin/bash
readonly PROJECT_KEY=MY_PROJECT
readonly PAGE_SIZE=500
jq --arg totalArg "$PAGE_SIZE" '.total = $totalArg' report.empty.json > report.json
jq --arg projectKey "${PROJECT_KEY}" '.project = $projectKey' report.empty.json > report.json
echo "Done"
But it set only key project. The key total is not changed.
Content of file report.json
{
"total": 0,
"project": "MY_PROJECT",
"Severity": [],
"issues": []
}
But I need to update BOTH KEYS.
The result must be:
{
"total": 500,
"project": "MY_PROJECT",
"Severity": [],
"issues": []
}

Answer 1

The second command reads from report.empty.json instead of the already-modified report.json.
You could chain the jq
jq --arg totalArg "$PAGE_SIZE" '.total = $totalArg' report.empty.json |
jq --arg projectKey "${PROJECT_KEY}" '.project = $projectKey' >report.json
But a better solution is to use just use one command.
jq --arg totalArg "$PAGE_SIZE" --arg projectKey "$PROJECT_KEY" '
.total = $totalArg | .project = $projectKey
' report.empty.json >report.json

Answer 2

My proposal for How to populate JSON values, using jq
Thinking about How to process arrays using jq, here is my modified version of your script. (Of course, you could keep empty.json out of script)...
#!/bin/bash
declare -r projectKey=MY_PROJECT
declare -ir pageSize=500
declare -a issueList=()
declare -i issueCnt=0
declare issueStr='' jqCmd='.project = $projArg | .total = $totArg | .issues=[ '
declare promptMessage='Enter issue (or [return] if none): '
while read -rp "$promptMessage" issue && [ "$issue" ];do
promptMessage='Enter next issue (or [return] if no more): '
issueCnt+=1
issueList+=(--arg is$issueCnt "$issue")
issueStr+="\$is$issueCnt, "
done
jqCmd+="${issueStr%, } ]"
jq --arg totArg "$pageSize" --arg projArg "$projectKey" \
"${issueList[#]}" "( $jqCmd )" <<-EoEmptyJson
{
"total": 0,
"project": "",
"Severity": [],
"issues": []
}
EoEmptyJson
Sample run (I want to add two issues):
./reportJson
Enter issue (or [return] if none): Foo
Enter next issue (or [return] if no more): Bar Baz
Enter next issue (or [return] if no more):
{
"total": "500",
"project": "MY_PROJECT",
"Severity": [],
"issues": [
"Foo",
"Bar Baz"
]
}

Answer 3

No answer (so far) accounts for the requirement that total be of type int. This can be accomplished by using --argjson instead of --arg. Here's my two cents:
jq --argjson total 500 --arg project "MY_PROJECT" '. + {$total, $project}' report.json
{
"total": 500,
"project": "MY_PROJECT",
"Severity": [],
"issues": []
}