Introduction to Index Mappings

In bleve, the IndexMapping describes how to your data model should be indexed.

Default IndexMapping

To get the default IndexMapping, simply call:

indexMapping := bleve.NewIndexMapping()

IndexMappings contain DocumentMappings for each of the different types of documents you want to support. Further, it contains a DefaultDocumentMapping that will be used for any type which does not have an explicit mapping.

Document Type

How does bleve know what type a document is?

  1. If your object implements the interface bleve.Classifier then bleve will use string returned by its Type() method.
  2. The IndexMapping has a setting called TypeField. You can set this to any document path, and if the value at that path is a string, that value will be used as the typed field. If you did not customize this setting the default is set to “_type”.
  3. If no type can be determined from 1 or 2, the type is set to the IndexMapping’s DefaultType. If you did not customize this setting the default is set to “_default”.

DocumentMappings

Now that we see how bleve will determine the type, we can provide a customized DocumentMapping for each type we’re interested in.

Let’s say we have a document type called blog. We can build a DocumentMapping for this type and configure the IndexMapping to use it:

blogMapping := bleve.NewDocumentMapping()
indexMapping.AddDocumentMapping("blog", blogMapping)

We can also set a catch-all mapping that will be used for any type that does not have an explicit mapping by setting the DefaultMapping field.

FieldMappings

Documents are hierarchical and contain named fields. These fields could be values or nested sub-documents. We customize the behavior for a named field by setting a DocumentMapping for it. Once we have a DocumentMapping for the named field, we can attach 0 or more FieldMappings to it. The FieldMappings describe how we want the field to be interpreted and what we want inserted into the index.

Let’s say our blog documents have a string field name and we want to use the English analyzer for this field.

nameFieldMapping := bleve.NewTextFieldMapping()
nameFieldMapping.Analyzer = "en"
blogMapping.AddFieldMappingsAt("name", nameFieldMapping)

Now let’s say our blog documents have a nested structure describing the author field field name and email. This time lets say we want index (default) but not store the author name. And we want to exclude the email address from the _all field.

author := bleve.NewDocumentMapping()
authorNameFieldMapping := bleve.NewTextFieldMapping()
authorNameFieldMapping.Store = false
author.AddFieldMappingsAt("name", authorFieldNameMapping)
authorEmailFieldMapping := bleve.NewTextFieldMapping()
authorEmailFieldMapping.IncludeInAll = false
author.AddFieldMappingsAt("email", authorEmailFieldMapping)
blog.AddSubDocumentMapping("author", author)

This shows use of a few of the other flags in a FieldMapping. Here is the list:

  • Index - index this field, defaults to true
  • Store - store this field, defaults to true
  • IncludeTermVectors - include term vectors for this field, defaults to true
  • IncludeInAll - includes this field in the compostie field named _all, defaults to true

Text Field specific options

  • Analyzer - the named analyzer to use on this field

There are multiple levels at which you can configure the Default Analyzer if an explicit one isn’t specified.

  1. Each DocumentMapping has a field DefaultAnalyzer. This means you can override the default analyzer for each sub-document.
  2. The IndexMapping also has a DefaultAnalyzer.

The DefaultAnalyzer configured with the longest path match to a field will be used.

Date Field specific options

  • DateFormat - the name of a DateTimeParser that will be used to parse a date stored as a string

You can configure a DefaultDateTimeParser in the IndexMapping object.

Understanding Default Type vs Default Mapping

When Bleve cannot figure out which type a particular document is, it is automatically assigned the DefaultType.

Once, Bleve has determined the type, it looks for a DocumentMapping matching this type name. If there is no explicitly configured DocumentMapping for this type, then the DefaultMapping is used.

The DefaultType will default to “_default”, and the DefaultMapping will default to an empty default DocumentMapping.

Consider an example from the beer-search sample application. The mapping describes two types “beer” and “brewery”. For each of these an explicit DocumentMapping is provided. If you attempt to index a document where the type field is missing, it will be assigned the type “_default”. Then Bleve looks to see if there is a mapping configured for “_default”. There is not, so then Bleve proceeds to use the DefaultMapping.