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Some theory first. When working with mongodb, we can basically talk about methods, filters and operators,

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not just for getting data but in general but especially for getting data filters and so on

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play an important role.

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So in the shell, we access the database with the db command, in a mongodb driver,

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this will differ slightly and you'll see it in the from shell to driver module towards the end of the

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course

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but there too, we will get access to the database and then to a collection in the database,

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the same can be done in the shell.

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Now then we can execute a method like find, insert also was a method, delete was a method,

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so everything which comes after a dot here and then has parentheses like this one is called a method,

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a method we execute on the collection in this case.

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Now we pass some data to this method,

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the parameters of the method, so to say. In find, the first argument or a parameter we can pass is a document

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describing what we'll look for,

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it has the format of a field name

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and then the value for that field name.

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Now you will learn that the value is quite flexible when finding data but in the end, this is the structure,

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fields and values

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and this is also what documents are all about, fields or keys however you want to name it and values

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for these names or fields.

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Now here, this argument for find happens to be a filter because find accepts a filter, it needs or it

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can use a filter to narrow down the set of documents

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it returns you.

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Here we got equality or a single value filter because we want to find all documents that have an age

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field where the age is exactly 32,

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so we're looking for equality here,

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this is a very simple filter but also one you'll use quite a lot.

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Now you can also use more complex filters where you for example see something like this as a value, where

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you have another document as a value which in turn has a value and where the field is then an operator

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and you can see or you can recognize operators by the dollar sign at the beginning.

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These are all reserved fields if you want to call them like this which are understood by mongodb

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.

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and this operation here as an example is called a range filter because it does not just filter for equality,

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instead this will look for all documents that have an age that is greater than, that's what the gt operator

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does, that is greater than the value, so greater than 30.

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This is how this works and what we will work with in this module, we'll learn a bunch of different operators

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and different ways of using them and different ways of filtering therefore.

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But in the end, this is always the structure you will recognize.