[#168,doc][m]: backend docs including overview and spec of how a backend should function.
* model docs get some improvement and moved to docs/models.markdown * change default layout to allow spec of where root is ...
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Rufus Pollock
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docs/backends.markdown
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122
docs/backends.markdown
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---
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layout: container
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title: Backends
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root: ../
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---
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<div class="page-header">
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<h1>
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Backends
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<small>Connect to data sources</small>
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</h1>
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</div>
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Backends come in 2 flavours:
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1. Loader backends - only implement fetch method. The data is then cached in a Memory.Store on the Dataset and interacted with there. This is best for sources which just allow you to load data or where you want to load the data once and work with it locally.
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2. Store backends - these support fetch, query and, if write-enabled, save. These are suitable where the backend contains a lot of data (infeasible to load locally - for examples a million rows) or where the backend has capabilities you want to take advantage of.
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Backend modules must implement the following API:
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{% highlight javascript %}
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__type__: 'name-of-backend' // e.g. elasticsearch
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// Initial load of dataset including initial set of records
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fetch: function(dataset)
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// Query the backend for records returning them in bulk.
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// This method will be used by the Dataset.query method to search the backend
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// for records, retrieving the results in bulk.
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query: function(queryObj, dataset)
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// Save changes to the backend
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save: function(changes, dataset)
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{% endhighlight %}
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Details of each function below. Note that:
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* Each backend function takes a dataset object. This is not a Dataset object
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but is simple JS object representation resulting from calling
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Dataset.toJSON().
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It is required because the Dataset attributes contain details of specific
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backend (e.g. url for ElasticSearch etc).
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* Each function returns a promise API object - that is something conforming to
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the jquery promise API and, in particular, having a done and fail function.
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### fetch: function(dataset)
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On success, promise callback must return an object with the following structure:
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{% highlight javascript %}
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{
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// (optional) Set of record data
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// Either an array of arrays *or* an array of objects corresponding to initial set of records for this object
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// May not provided if data only returned by query
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records: [...]
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// (optional) Set of field data
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// Either an array of string or an array of objects corresponding to Field specification (see `Field` above)
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fields: { ... } // as per recline.Model.Field
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// (optional) metadata fields to set on the Dataset object
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metadata: { title: ..., id: ... etc }
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// boolean indicating whether to use a local memory store for managing this dataset
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useMemoryStore:
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}
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{% endhighlight %}
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### query: function(queryObj, dataset)
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`queryObj`: JS object following <a href="models.html#query-structure">Query specification</a> above.
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#### Callbacks
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On success must return a 'QueryResult' object which has the following structure:
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{% highlight javascript %}
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{
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// total number of results (can be null)
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total: ...
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// one entry for each result record
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hits: [
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{
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// JS object that can be used to initialize a Record object
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}
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],
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// (optional)
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facets: {
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// facet results (as per <http://www.elasticsearch.org/guide/reference/api/search/facets/>)
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}
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}
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{% endhighlight %}
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The QueryResult is partially modelled on ElasticSearch - see <a
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href="https://github.com/okfn/recline/issues/57">this issue for more
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details</a>.
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### save: function(changes, dataset)
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<div class="alert alert-warning">The save function is still being revised and
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its API and arguments are subject to change</div>
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`changes`: an object with the following structure:
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{% highlight javascript %}
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{
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creates: [ record.toJSON(), record.toJSON(), ... ]
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updates: [ ... ]
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deletes: [ ... ]
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}
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{% endhighlight %}
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Each key has an array of records (as simple JS objects resulting from a call to
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Record.toJSON()) that are in that state.
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The backend should take appropriate actions for each case.
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250
docs/models.markdown
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250
docs/models.markdown
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---
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layout: container
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title: Models
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root: ../
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---
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<div class="page-header">
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<h1>
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Models
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</h1>
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</div>
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Models help you structure your work with data by providing some standard
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objects. The key ones are Dataset and Record -- a Dataset being a collection of
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Records. Additionally, there is a a Field object for describing the columns of
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a Dataset, a Query object for describing queries, and a Facet object for
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holding summary information about a Field (or multiple Fields).
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# Models
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All the models are Backbone models, that is they extend Backbone.Model. Note,
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however that they do not 'sync' (load/save) like normal Backbone models.
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## Dataset
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A Dataset is *the* central object in Recline. Standard usage is:
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{% highlight javascript %}
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var dataset = new recline.model.Dataset({
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// general metadata e.g.
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id: ...
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title: ...
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// information about data source e.g.
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url: http://url.to.my.data.endpoint/
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// backend string or object
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backend: the backend we are using - see below
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});
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// initialize dataset with data from the backend.
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dataset.fetch();
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// we will now have the following (and more) set up - see below for details
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dataset.fields // collection of Fields (columns) for this Dataset
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dataset.currentRecords // collection of Records resulting from latest query
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dataset.docCount // total number of Records in the last query
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{% endhighlight %}
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### Key Attributes
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* currentRecords: a collection of `Record`s currently loaded for viewing
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(updated by calling query method) - note that this need <strong>not</strong>
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be all the records in the dataset (for example, you may have connected to a
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source where the complete dataset contains a million records but you have
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only loaded a 1000 records)
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* fields: (aka columns) is a Backbone collectoin of `Field`s listing all the
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fields on this Dataset (this can be set explicitly, or, will be set by
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Dataset.fetch()
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* docCount: total number of records in this dataset
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* backend: the Backend (instance) for this Dataset.
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* queryState: a `Query` object which stores current queryState. queryState may
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be edited by other components (e.g. a query editor view) changes will trigger
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a Dataset query.
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* facets: a collection of `Facet`s
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### Querying
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{% highlight javascript %}
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dataset.query(queryObj)
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{% endhighlight %}
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`queryObj` an object following the <a href="#query-structure">query
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pecification below</a>.
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<h2 id="record">Record (aka Row)</h2>
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A Record is a single entry or row in a dataset. A Record needs little more than
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what is provided by the standard Backbone Model object. In general, you will
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never create a Record directly -- they will get created for you by Datasets
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from query results.
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<h2 id="field">Field (aka Column)</h2>
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A Field should have the following attributes as standard:
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{% highlight javascript %}
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var field = new Field({
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// a unique identifer for this field- usually this should match the key in the records hash
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id: 'my-field-id'
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// (optional: defaults to id) the visible label used for this field
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label: 'My Field Name',
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// (optional: defaults to string) the type of the data in this field.
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// Should be a string as per type names defined by ElasticSearch - see
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// Types list on <http://www.elasticsearch.org/guide/reference/mapping/>
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type: 'string',
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// (optional - defaults to null) used to indicate how the data should be
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// formatted. See below.
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format: null,
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// (default: false) attribute indicating this field has no backend data but
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// is just derived from other fields (see below).
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is_derived: false
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{% endhighlight %}
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#### Rendering, types and formats
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One can customize the rendering of fields in the user interface and elsewhere
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by setting a renderer function on the field. You do this by setting a field
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attribute:
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{% highlight javascript %}
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myfield.renderer = myRenderFunction;
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{% endhighlight %}
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Your renderer function should have the following signature:
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function(value, field, record)
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Where the arguments passed in are as follows:
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* `value`: the value of the cell (record value for this field)
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* `field`: corresponding `Field` object
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* `record : is the `Record` object (as simple JS object)
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Note that implementing functions can ignore arguments (e.g. function(value)
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would be a valid formatter function).
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To guide the behaviour of renderers we have type and format information.
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Example types and formats are:
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* type=date, format=yyyy-mm-dd
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* type=float, format=percentage
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* type=string, format=markdown (render as markdown if Showdown available)
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Default renderers are provided - see the source for details, but a few examples
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are:
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* type = string
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* no format provided: pass through but convert http:// to hyperlinks
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* format = plain: do no processing on the source text
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* format = markdown: process as markdown (if Showdown library available)
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* type = float
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* format = percentage: format as a percentage
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#### Derived fields
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Some fields may be 'dervied' from other fields. This allows you to define an
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entirely new value for data in this field. This provides support for a)
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'derived/computed' fields: i.e. fields whose data are functions of the data in
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other fields b) transforming the value of this field prior to rendering.
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To use derived fields set a `deriver` function on the Field. This function will
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be used to derive/compute the value of data in this field as a function of this
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field's value (if any) and the current record. It's signature and behaviour is
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the same as for renderer.
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<h2 id="query">Query</h2>
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Query instances encapsulate a query to the backend (see <a
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href="backend/base.html">query method on backend</a>). Useful both
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for creating queries and for storing and manipulating query state -
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e.g. from a query editor).
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<h3 id="query-structure">Query Structure and format</h3>
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Query structure should follow that of [ElasticSearch query
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language](http://www.elasticsearch.org/guide/reference/api/search/).
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**NB: It is up to specific backends how to implement and support this query
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structure. Different backends might choose to implement things differently
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or not support certain features. Please check your backend for details.**
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Query object has the following key attributes:
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* size (=limit): number of results to return
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* from (=offset): offset into result set - http://www.elasticsearch.org/guide/reference/api/search/from-size.html
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* sort: sort order - <http://www.elasticsearch.org/guide/reference/api/search/sort.html>
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* query: Query in ES Query DSL <http://www.elasticsearch.org/guide/reference/api/search/query.html>
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* filter: See filters and <a href="http://www.elasticsearch.org/guide/reference/query-dsl/filtered-query.html">Filtered Query</a>
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* fields: set of fields to return - http://www.elasticsearch.org/guide/reference/api/search/fields.html
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* facets: specification of facets - see http://www.elasticsearch.org/guide/reference/api/search/facets/
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Additions:
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* q: either straight text or a hash will map directly onto a [query_string
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query](http://www.elasticsearch.org/guide/reference/query-dsl/query-string-query.html)
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in backend
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* Of course this can be re-interpreted by different backends. E.g. some may
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just pass this straight through e.g. for an SQL backend this could be the
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full SQL query
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* filters: array of ElasticSearch filters. These will be and-ed together for
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execution.
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#### Examples
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<pre>
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{
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q: 'quick brown fox',
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filters: [
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{ term: { 'owner': 'jones' } }
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]
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}
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</pre>
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<h2>Facet <small>– Store summary information (e.g. values and counts) about a field obtained by some 'faceting' or 'group by' method</small>
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</h2>
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Structure of a facet follows that of Facet results in ElasticSearch, see:
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<http://www.elasticsearch.org/guide/reference/api/search/facets/>
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Specifically the object structure of a facet looks like (there is one
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addition compared to ElasticSearch: the "id" field which corresponds to the
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key used to specify this facet in the facet query):
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{% highlight javascript %}
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{
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id: "id-of-facet",
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// type of this facet (terms, range, histogram etc)
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\_type : "terms",
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// total number of tokens in the facet
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total: 5,
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// @property {number} number of records which have no value for the field
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missing : 0,
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// number of facet values not included in the returned facets
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other: 0,
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// term object ({term: , count: ...})
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terms: [ {
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"term" : "foo",
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"count" : 2
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}, {
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"term" : "bar",
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"count" : 2
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}, {
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"term" : "baz",
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"count" : 1
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}
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]
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}
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{% endhighlight %}
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