How to hook to update instead of deleting and stop creating

[pwFoo]

Hi,

try to implement two hooks

1. If entry is deleted, update object property to 'null' (redirect from deleting hook to a database update?)
2. Skip db save if hook creating validation fails (tried to return false, empty object, undefined and replaced obj...)

Modify obj works fine, but stop db transaction fails. And I have no idea, how to trigger an update from inside of the deleting hook and skip deleting entry.
Searched docs and internet, but haven't found such examples. Anyone maybe could help me to implement such two hooks?

[pwFoo]

Found the solution for skip creating by transaction.abort() inside of creating hook.
I think about deleting should the half way to redirect deleting to updating... need to find a way to run modify from inside of deleting hook callback.

[pwFoo]

Tried different ways to run a table.put() from inside of the hook...
I read about problems with async calls from inside hooks (that's why I moved from crypto api to tweetnacl), but thought would be no problem if I'm not need to await it?

hookDeleting = (primKey, obj, transaction) => {
                primKey = primKey.split('+')
                obj = { id: primKey[0], key: primKey[1], val: "MODIFIED_INSTEAD_DELETED!" }
                let table = transaction.table('data')
                transaction.abort()
                table.put(obj)
                logger("HookDeleting", primKey, obj, transaction, table)
            }

Abort transaction works, but need to update the obj.val and save it.

[pwFoo]

Fixed my hook... works now

hookDeleting = (primKey, obj, transaction) => {
                logger("HookDeleting", primKey, obj, transaction)
                transaction.on('abort', () => {
                    primKey = primKey.split('+')
                    obj = { id: primKey[0], key: primKey[1], val: "MODIFIED_INSTEAD_DELETED!" }
                    window['$'].data.put(obj)
                    console.log("DEBUG", obj)
                })
                transaction.abort()
            }

[dfahlander]

That looks like a nasty hack as it relies on something on window to be there and it does another operation on abort.

You should try middlewares instead if you care about your code quality, debugging and understanding why the code does a certain thing.

[pwFoo]

Hi @dfahlander,

moved away from window by bind table to callback in my constructor:

this.data.hook('deleting', hookDeleting.bind(this.data))

hookDeleting = function(primKey, obj, transaction) {
    primKey = primKey.split('+')
    obj = { id: primKey[0], key: primKey[1], val: null }
    console.log("HookDeleting", 'RedirectToModify', primKey, obj, transaction, this)
    transaction.on('abort', () => {    
        this.put(obj)
    })
    transaction.abort()
},

[dfahlander]

your use case requires using middlewares instead of hooks. https://dexie.org/docs/Dexie/Dexie.use()

With middlewares you can change the behavior completely and support async actions such as using put to downlevelTable instead of the requested delete operation.

[pwFoo]

Thanks, I read about, but not understand how to use or implement my use case with it. I'll take a look again and do some tests.

In words I try to

• update / create (verified) signed items as "synced in" from extern / remote
• validate and sign changed / created items before save
• verify signature of items on read
• redirect delete to update obj.val = null

hookReading = (obj) => {
    console.log("HookReading", obj)
    if(obj.sig && verifySignature(obj)) {
        console.log("--> VERIFIED", obj)
        return obj
    } else {
        console.log("--> ERROR: VERIFY FAILED", obj)
        return false
    }
},
// bind context key pair
hookCreating = function(primKey, obj, transaction) {
    console.log("HookCreating", primKey, obj, transaction, this) 
    if(obj.val === undefined || this.priv === '') {
        console.log("ERROR, skip saving...", obj.val, this)
        transaction.abort()
        return false 
    } else if(obj.sig && verifySignature(obj)) {
        console.log("--> remote SYNCED", obj)
        return obj
    } else {
        Object.assign(obj, { ts: Date.now(), pub: this.pub })
        obj.sig = signDetached(JSON.stringify(obj), this.priv)
        console.log("--> local SAVED", obj)
        return obj
    } 
},
// bind context key pair
hookUpdating = function(modifications, primKey, obj, transaction) {
    console.log("HookUpdating", modifications, primKey, obj, transaction, this)
    if(modifications.val === undefined || this.priv === '') {
        console.log("ERROR, skip saving...", modifications.val, this)
        transaction.abort()
        return false 
    } else if(modifications.ts > obj.ts && verifySignature(Object.assign(obj, modifications))) {
        console.log("--> remote SYNCED", modifications, obj)
        return obj
    } else {
        Object.assign(obj, modifications, { ts: Date.now(), pub: this.pub })    
        delete obj.sig
        obj.sig = signDetached(JSON.stringify(obj), this.priv)
        console.log("--> local SAVED", modifications, obj)
        return obj
    } 
},
// bind context table
hookDeleting = function(primKey, obj, transaction) {
    primKey = primKey.split('+')
    obj = { id: primKey[0], key: primKey[1], val: null }
    console.log("HookDeleting", 'RedirectToModify', primKey, obj, transaction, this)
    transaction.on('abort', () => {    
        this.put(obj) 
    })
    transaction.abort()
},

[pwFoo]

Looks like create / update is working fine, but need to distinguish between create / update (values arry and type = put) and delete (type delete).

Would you suggest another way than

if (myRequest.type === 'delete') {
 // delete ...
} else {
 // create or update....
}

But how to redirect delete to update transaction?

My middleware test code

            myCustomMiddleware = {
                stack: 'dbcore',
                name: 'MyCustomMiddleware',
                create: (downlevelDatabase) => ({
                    ...downlevelDatabase,
                    table: (tableName) => {
                        const downlevelTable = downlevelDatabase.table(tableName)
                        if(tableName === 'data') {
                            console.log("DEBUG MIDDLEWARE", downlevelTable)
                            return {
                                ...downlevelTable,
                                mutate: (req) => {
                                    const myRequest = {...req}
                                    console.log("DEBUG MUTATE", myRequest.type, myRequest)
                                    // Do things before mutate, then
                                    if(myRequest.type === 'delete') {
                                        // redirect delete ... ???
                                    } else {
                                        myRequest.values.forEach((item, index, arr) => {
                                            if(item.sig && verifySignature(item)) {
                                                console.log("--> SYNC IN", item)
                                            } else if(item.val === undefined) {
                                                console.log("--> ERROR, 'val' missing!", item)
                                                delete arr[index]
                                            } else if(pair.priv) {
                                                // verifiy id, key, val isset
                                                // sign
                                                item.ts = Date.now()
                                                item.pub = pair.pub
                                                item.sig = SEA.signDetached(JSON.stringify(item), pair.priv)
                                                console.log("--> SAVE CHANGE", item)
                                            } else {
                                                console.log("--> ERROR, Guest?", item, pair)
                                            }
                                        })
                                    }
                                    // call downlevel mutate:
                                    return downlevelTable.mutate(myRequest).then(res => {
                                        // Do things after mutate
                                        const myResponse = {...res}
                                        // Then return your response:
                                        return myResponse;
                                    })
                                }
                            }
                        } else {
                            return downlevelTable   // default table method...
                        }
                    }
                })
            }

[pwFoo]

@dfahlander How hooking read from middleware? Is there a similiar way like mutate to handle all read requests at once?

[pwFoo]

Hi @dfahlander,

so best way is middleware instead of old hook system? Asking because of planned change subscriptions for matching keys.

Looks like I found how to implement my features with middleware by query and mutate:

MyCustomMiddleware = {
                stack: 'dbcore',
                name: 'MyCustomMiddleware',
                create: (downlevelDatabase) => ({
                    ...downlevelDatabase,
                    table: (tableName) => {
                        const downlevelTable = downlevelDatabase.table(tableName)
                        if(tableName === 'data') {
                            console.log("DEBUG MIDDLEWARE", downlevelTable)
                            return {
                                ...downlevelTable,
                                query: (req) => {
                                    console.log("DEBUG QUERY:BEFORE", req)
                                    return downlevelTable.query(req).then(res => {
                                        console.log("DEBUG QUERY_AFTER", res)
                                        // Do things after query
                                        const myResponse = {...res}
                                        myResponse.result.forEach((item, index, arr) => {
                                            if(verifySignature(item)) {
                                                console.log("--> verified signature", item)
                                            } else {
                                                delete arr[index]
                                            }
                                        })
                                        // Then return your response:
                                        return myResponse;
                                    })
                                },
                                mutate: (req) => {
                                    const myRequest = {...req}
                                    console.log("DEBUG MUTATE", myRequest.type, myRequest)
                                    // Do things before mutate, then
                                    if(myRequest.type === 'delete') {
                                        // redirect delete ... ???
                                    } else {
                                        myRequest.values.forEach((item, index, arr) => {
                                            if(item.sig && verifySignature(item)) {
                                                console.log("--> SYNC IN", item)
                                            } else if(item.val === undefined) {
                                                console.log("--> ERROR, 'val' missing!", item)
                                                delete arr[index]
                                            } else if(pair.priv) {
                                                // verifiy id, key, val isset
                                                // sign
                                                item.ts = Date.now()
                                                item.pub = pair.pub
                                                item.sig = SEA.signDetached(JSON.stringify(item), pair.priv)
                                                console.log("--> SAVE CHANGE", item)
                                            } else {
                                                console.log("--> ERROR, Guest?", item, pair)
                                            }
                                        })
                                    }
                                    // call downlevel mutate:
                                    return downlevelTable.mutate(myRequest).then(res => {
                                        // Do things after mutate
                                        const myResponse = {...res}
                                        // Then return your response:
                                        return myResponse;
                                    })
                                }
                            }
                        } else {
                            return downlevelTable   // default table method...
                        }
                    }
                })
            }