Booking Rules are Javascript validations that you can attach to the Booking creation event which is triggered when a booking is created on the schedule board or the schedule assistant.
To create a Booking Rule, Field Service > Administration, and then choose Booking Rules.

What we need to do is attach a JS web resource with the Booking rule. The JS web resource should have a function which takes in the context and is called when a Resource requirement is dragged and dropped on to the Schedule board or the assistant.
Let’s see some code, in this example we are restricting creating of a Booking on the basis of how many bookings are already being created for a Resource.
function validateRules(sbContext) {
debugger;
var ruleResult = {};
var resourceReqId = '';
if (sbContext.newValues.ResourceRequirementId != undefined) {
resourceReqId = sbContext.newValues.ResourceRequirementId;
}
else if (sbContext.newValues.ResourceScheduleSource != undefined && sbContext.newValues.ResourceScheduleSource == 690970004) {//SA
var rr = Xrm.Page.getAttribute('msdyn_resourcerequirement');
if (rr != null && rr.getValue() != null && rr.getValue().length > 0) {
resourceReqId = rr.getValue()[0].id;
}
}
if (resourceReqId == '') {
console.log('RR is null. Exiting..');
ruleResult.IsValid = true;
ruleResult.Message = “No RR”;
ruleResult.Type = ‘success’;
return ruleResult;
}
resourceReqId = resourceReqId.replace(‘{‘, ”).replace(‘}’, ”);
var resourceId = sbContext.newValues.ResourceId;
var startTime = sbContext.newValues.StartTime;
var endTime = sbContext.newValues.EndTime;
var hearingType = ”;
var req = new XMLHttpRequest();
req.open(“GET”, encodeURI(Xrm.Page.context.getClientUrl() + ‘/api/data/v8.2/msdyn_resourcerequirements?$filter=msdyn_resourcerequirementid eq ‘ + resourceReqId + ‘&$expand=new_wa_case($select=wa_hearingtype)’), false);
req.setRequestHeader(“Accept”, “application/json”);
req.setRequestHeader(“Content-Type”, “application/json;charset=utf-8”);
req.setRequestHeader(“OData-MaxVersion”, “4.0”);
req.setRequestHeader(“OData-Version”, “4.0”);
req.setRequestHeader(“Prefer”, “odata.include-annotations=OData.Community.Display.V1.FormattedValue”);
req.send();
if (req.readyState === 4) {
req.onreadystatechange = null;
if (req.status === 200) {
var result = JSON.parse(req.response);
hearingType = result.value[0].new_wa_case[‘wa_hearingtype’];
if (hearingType == null) {
hearingType = 953860001; // Motion as default
console.log(‘motion set as default’);
}
console.log(hearingType);
//————————————————
var dt = new Date(startTime).toISOString();
var st = dt.substr(0, dt.indexOf(‘T’)) + ‘T00:00:00Z’;
var et = dt.substr(0, dt.indexOf(‘T’)) + ‘T23:59:59Z’; //2018-07-17T11:59:59Z
console.log(dt); // today’s date
var req = new XMLHttpRequest();
req.open(“GET”,
encodeURI(Xrm.Page.context.getClientUrl() +
‘/api/data/v8.2/bookableresourcebookings?$select=bookableresourcebookingid,starttime,endtime&$expand=Resource($select=wa_jurytrialhearinglimit,wa_motion)&$filter=_resource_value eq ‘ +
resourceId +
‘ and wa_hearingtype eq ‘ +
hearingType +
‘ and starttime gt (‘ + st + ‘) and endtime lt (‘ + et + ‘)’),
false);
req.setRequestHeader(“Accept”, “application/json”);
req.setRequestHeader(“Content-Type”, “application/json;charset=utf-8”);
req.setRequestHeader(“OData-MaxVersion”, “4.0”);
req.setRequestHeader(“OData-Version”, “4.0”);
req.setRequestHeader(“Prefer”, “odata.include-annotations=OData.Community.Display.V1.FormattedValue”);
req.send();
if (req.readyState === 4) {
req.onreadystatechange = null;
if (req.status === 200) {
var res = JSON.parse(req.response);
var data = res.value;
ruleResult.IsValid = true;
ruleResult.Message = “Validation succeeded”;
ruleResult.Type = ‘success’;
if (data.length > 0 && data[0].Resource != null) { // Court Room
var juryLimit = data[0].Resource.wa_jurytrialhearinglimit;
var motionLimit = data[0].Resource.wa_motion;
console.log(data, data.length, juryLimit, motionLimit);
var isDone = false;
for (var i = 0; i = new Date(data[i].starttime) && startTime = juryLimit) {
ruleResult.IsValid = false;
ruleResult.Message = ‘Jury Hearing capacity reached. Bookings not allowed.’;
ruleResult.Type = ‘error’;
} else if (hearingType == 953860001 && data.length >= motionLimit) {
ruleResult.IsValid = false;
ruleResult.Message = ‘Motion Hearing capacity reached. Bookings not allowed.’;
ruleResult.Type = ‘error’;
}
}
}
} else {
console.log(req.statusText);
}
}
}
else {
console.log(req.statusText);
}
}
return ruleResult;
}