Indexes: Multi-Map Indexes

Multi-Map indexes allow you to index data from multiple collections e.g. polymorphic data (check the example) or any common data between types.

AddMap

addMap() method is used to map fields from a single collection e.g. Dogs.

Let's assume that we have Dog and Cat classes, and both of them inherit from the class Animal:

class Dog extends Animal { }

class Cat extends Animal { }

class Animal {
    constructor(name) {
        this.name = name;
    } 
}

Now we can define our index using addMap in the following way:

class Animals_ByName extends AbstractMultiMapIndexCreationTask {
    constructor() {
        super();

        this.addMap(`docs.Cats.Select(c => new {     
            name = c.name 
        })`);

        this.addMap(`docs.Dogs.Select(d => new {     
            name = d.name 
        })`);
    }
}

const results = await session
    .query({ indexName: "Animals/ByName" })
    .whereEquals("name", "Mitzy")
    .all();

from index 'Animals/ByName'
where Name = 'Mitzy'

Indexing Polymorphic Data

Please read more in our dedicated article on indexing polymorphic data. This article can be found here.

Searching Across Multiple Collections

Another great application of Multi-Map indexes is smart-search. To search for products, companies, or employees by their name, you need to define the following index:

class Smart_Search extends AbstractMultiMapIndexCreationTask {

    constructor() {
        super();

        this.addMap(`docs.Companies.Select(c => new {     
            id = Id(c),     
            content = new string[] {         
                c.name     
            },     
            displayName = c.name,     
            collection = this.MetadataFor(c)["@collection"] 
        })`);


        this.addMap(`docs.Products.Select(p => new {     
            id = Id(p),     
            content = new string[] {         
                p.name     
            },     
            displayName = p.name,     
            collection = this.MetadataFor(p)["@collection"] 
        })`);

        this.addMap(`docs.Employees.Select(e => new {     
            id = Id(e),     
            content = new string[] {         
                e.firstName,         
                e.lastName     
            },     
            displayName = (e.firstName + " ") + e.lastName,     
            collection = this.MetadataFor(e)["@collection"] 
        })`);

        // mark 'content' field as analyzed which enables full text search operations
        this.index("content", "Search");

        // storing fields so when projection (e.g. ProjectInto)
        // requests only those fields
        // then data will come from index only, not from storage
        this.store("id", "Yes");
        this.store("displayName", "Yes");
        this.store("collection", "Yes");
    }
}

and query it using:

const results = await session
    .query({ indexName: "Smart/Search" })
    .search("Content", "Lau*")
    .selectFields([ "id", "displayName", "collection" ])
    .all();

for (const result of results) {
    console.log(result.collection + ": " + result.displayName);
    // Companies: Laughing Bacchus Wine Cellars
    // Products: Laughing Lumberjack Lager
    // Employees: Laura Callahan
}

Remarks