Add deprecation warning for default strictQuery

[vkarpov15]

Prerequisites

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Issue

We're planning on switching strictQuery back to false in Mongoose 7, see #11861. We should add a deprecation warning to encourage devs to add mongoose.set('strictQuery', false) in their projects to prepare for this change.

[lpizzinidev]

@vkarpov15 @hasezoey
When should the warning be displayed?
On database connection?

[hasezoey]

When should the warning be displayed?

i would guess under the following conditions:
on query or on connection if strictQuery is not manually set and maybe only if it would affect the query by having it true

[vkarpov15]

I think only on database connection. We're changing the default global option, so printing a warning if strictQuery isn't set on a query doesn't seem like the way to go.

[mohit4bug]

import mongoose from "mongoose";


// ADD THIS IS YOUR CONNECTION FILE
mongoose.set('strictQuery', true);

// CONNECTION
mongoose.connect("mongodb://0.0.0.0:27017/<dbname>", {
    useNewUrlParser: true,
    useUnifiedTopology: true,
}).then(console.log("connected to db!"))
    .catch(e => console.log(e))