db={"emailtemplates":[{"name":"WELCOME-01","channel":"email","status":"active","title":"Hello, welcome {firstname} {lastnane}","parameters":[{"name":"firstname","type":"string","required":true},{"name":"lastname","type":"string","required":true}],"body":"Dear {firstname}, Welcome to the club"},{"name":"GOODBYE-01","channel":"email","status":"active","title":"Hello, welcome {firstname} {lastnane}","parameters":[{"name":"firstname","type":"string","required":true},{"name":"lastname","type":"string","required":true}],"body":"Dear {firstname}, were sorry to see you go"},{"name":"YOURE-FIRED-01","channel":"email","status":"active","title":"Hello, welcome {firstname} {lastnane}","parameters":[{"name":"firstname","type":"string","required":true},{"name":"lastname","type":"string","required":true}],"body":"Dear {firstname}, Pack your stuff and go"}],"emails":[{"templateName":"WELCOME-01","recipient":"john.doe@gmail.com","parameters":{"firstName":"John","lastName":"Doe"}},{"templateName":"WELCOME-01","recipient":"david.chappelle@gmail.com","parameters":{"firstName":"David","lastName":"Chappelle"},},{"templateName":"GOODBYE-01","recipient":"the.joker@gmail.com","parameters":{"firstName":"The","lastName":"Joker"}}]}

db.emailtemplates.aggregate([{$match:{channel:"email"}},{$lookup:{from:"emails",let:{templateName:"$templateName",name:"$name"},pipeline:[{$match:{$expr:{$eq:["$templateName","$$name"]}}},{$project:{"templateName":"$templateName","name":"$name"}}],as:"emails"}}])