# Using data sources in simulations

### Attaching a data source to a simulation

You can upload a csv file when editing your simulation from the Simulation tab.

You can both query data from a CSV data source as well as manipulate data within a data source by adding to it and deleting from it. Hoverfly supports a number of templating methods for simple read, update and delete functions. In addition Hoverfly supports a templating function that allows simple SQL like commands for SELECT, UPDATE and DELETE.

Note that you cannot edit the data sources on a simulation already running on a service. You need to add and remove data sources from the master copy of the simulation, and then start a service running a copy of that simulation.

<div data-full-width="false"><figure><img src="/files/4Ds8Oab95QALmZbsACMM" alt=""><figcaption><p>Add CSV data sources</p></figcaption></figure></div>

### Looking up a data value from within the response template

To use the data in the csv file, you need to use the {{ csv }} templating function.

```handlebars
{{csv '<data-source-name>' '<key-column>' '<key-value>' '<return-column>'}}
```

So for example given a data source named "products" with the following csv structure:

<figure><img src="/files/KGc0RcY55PIvrEaZZHxJ" alt=""><figcaption></figcaption></figure>

You can use the following syntax to render the word "shirt" in a response template (note the use of single quotes):

```handlebars
{{csv 'products' 'productId' '101' 'productName'}}
```

Or if for example the productId was provided at position 1 on the path:

```handlebars
{{csv 'products' 'productId' (Request.Path.[1]) 'productName'}}
```

Or if you needed to loop over some JSON array of productIds from the request body and render back data doing lookups for each productId:

```handlebars
{{#each (Request.Body 'jsonpath' '$.products')}}  
ProductId {{this}} is {{csv 'products' 'productId' this 'productName'}}
{{/each}}
```

There are a number of functions to allow querying, updating, deleting and inserting data into the csv data sources. You can read more about them below:

[<mark style="color:yellow;">Querying csv data sources</mark>](/create-simulations/using-data-sources-in-simulations/querying-data-sources.md)

[<mark style="color:yellow;">Updating csv data sources</mark>](/create-simulations/using-data-sources-in-simulations/updating-data-in-data-sources.md)

[<mark style="color:yellow;">Deleting data from csv data sources</mark>](/create-simulations/using-data-sources-in-simulations/deleting-data-from-data-sources.md)

[<mark style="color:yellow;">Inserting data into csv data sources</mark>](/create-simulations/using-data-sources-in-simulations/inserting-data-into-a-data-source.md)

[<mark style="color:yellow;">Guidance on using the SQL like syntax</mark>](/create-simulations/using-data-sources-in-simulations/guidance-on-using-the-sql-like-syntax.md)


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