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instead of writing literally delete from collection
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where title equals Farmers Working At Dawn, I
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could say update the deleted column of collections, where the title is Farmers
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Working At Dawn, and make it not 0, but 1.
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Now, I've marked this item as deleted.
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I could run a query that excludes deleted items,
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but this row is still around in my table.
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So let's try implementing this idea of a soft deletion
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inside of our collections table so that we
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don't lose records of things that actually had in our collection.
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I'll come back to my computer here, and let's work
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on altering our table for collections here.
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If I type dot schema collections--
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dot schema collections, you should see I have a table "collections," and also
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the triggers associated with it.
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What I don't have yet in collections, if I go over here and show you,
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I don't have a deleted column.
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I have ID, title, accession number, and acquired, but I don't have deleted.
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So as you learned last week, we can use alter table
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to add a column to our collections table, and by default, make the value
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0.
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So let's try that.
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I'll go back to my environment, and now I'll run alter table.
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I might say alter table, and a table I want to alter, which is "collections."
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Now I want to add the column "deleted" to collections,
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and I want to make this type integer, so our whole numbers
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whether positive or negative, and the default value will be 0 in this case.
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Now, I'll hit Enter, and if I type dot schema collections,
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I should see I have my very own deleted column inside of collections.
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If I type, for instance, select star from collections semicolon,
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I'll see that by default, all of these values are 0 in my new deleted column.
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So instead of trying to literally delete from collections,
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I could instead just update it.
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I could say take the updated column, and flip it from a 0 to a 1.
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Let me try update collections and set the deleted column
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equal to 1, where let's say the title equals Farmers Working At Dawn.
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And my query wraps here, but it should still work just fine.
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I'll hit semicolon, Enter.
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Now, I didn't use delete from.
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I used update.
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If I select star from collections semicolon here,
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I'll see, well, Farmers Working At Dawn is in this table,
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but technically-- at least we marked it as deleted.
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So it seems now, I don't want to use just select star from collections
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to see what's inside my collection.
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I want to apply a filter to remove those that have
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a deleted value that's not equal to 0.
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Let's try this.
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I'll say select star from collections where deleted does not equal 1.
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If I hit semicolon here, what do I see?
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Only those values that are not deleted.
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I could go ahead and find them.
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I could say maybe select star from collections where deleted actually
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is 1.
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Really equals 1 like this, and now I see all those rows
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that I marked as deleted.
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Now this has some advantages.
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One of them is we keep data around.
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We don't actually formally delete it.
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We can still recover it later on, but it also has some tricky ethical questions,
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too.
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Like it's OK if we're talking about artwork here,
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but if you're talking about user data, is it right to only soft delete it
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if they ask you to delete it?
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Particularly in conversation with new frameworks like GDPR,
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and the right to be forgotten, and so on, it's up to you
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as a programmer to make the right decision here.
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When should you find data that [INAUDIBLE] and actually delete it,
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or when is it better to just soft delete it and keep it around
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in case you need it for later?
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So we'll end here on this note where if I say select star from collections,
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and I want to find those only where deleted is not equal to 0 like this--
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or not equal to 1, this gives me back all of the items that are not deleted.
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But wouldn't it be nice if I could actually
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run a query on some brand new temporary table that actually only will ever have
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those items that are not soft deleted?
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Turns out, we can do that with an idea called views,
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and we'll see those in much more depth next week.
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We'll see you then.
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[MUSIC PLAYING]
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SPEAKER 1: Hello and welcome for Lecture 3 in React Native.
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So previous lecture we talked about a bunch of different topics;
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one being classes and how ES6 allows you to write classes.
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React, we talked about the library by Facebook
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that allows you to write declarative programming.
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We talked about what imperative and declarative programming were
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and how React allows you to write declaratively.
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We talked about props, which are basically an object that
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are passed down to elements.
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We talked about state, which is a management system for allowing you
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to track state in a class component.
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We implemented the to do app in React and then we teased at something
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called React Native.
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And so this lecture we'll be talking a lot about React Native.
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React Native is a framework that relies on React Core.
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And so a lot of the paradigms that apply to React also apply to React Native.
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And it allows us to build mobile apps using only JavaScript.
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And so, as the React team like to say when this was released,
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you can learn once and write everywhere.
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And so React Native supports iOS and Android,
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