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I am trying to figure out how to add a date search to assign the correct warranty to a record. The code below assigns the record by product right now but I need to add the record with the correct cut-in and cut -off dates and by product as well. any help would be greatly appreciated.

trigger Trigger_UpdateWarranties on Unit__c (before insert, before update ) {

// Step 1: Create a set of all products of Units to query
Set allwrnty = new Set();

for (Unit__c newUnit : Trigger.new) {
if (newUnit.Product__c != null) {
allwrnty.add(newUnit.Product__c); }
}

// Step 2: Query for all the Units in Step 1
List potentialproduct = [SELECT Id, Name, Product__c FROM Warranty__c
WHERE Product__c IN :allwrnty];

// Step 3: Make a Map that lets you search for units by product
Map wrntyMap = new Map();
for (Warranty__c w : potentialproduct) {
wrntyMap.put(w.Product__c, w);
}
// Step 4: Get the matching Warranty in the Map by product!
for (Unit__c newUnit : Trigger.new) {
if (newUnit .Warranty_Type__c == null) {
Warranty__c product = wrntyMap.get(newUnit.Product__c);
if (product != null) {
newUnit.Warranty_Type__c = product.Id;
}
}
}

}