Loading ECSchemas from XML Files

To load EC Schemas from XML files, you need to locate these files on the file system. The Bentley package @itwin/ecschema-locaters provides locater classes that implement ISchemaLocater to locate schemas in a given SchemaContext.

PublishedSchemaXmlFileLocater

The Bentley provided @itwin/core-backend package includes a set of standard schema assets accessible at KnownLocations.nativeAssetsDir.

While the SchemaXmlFileLocater can locate schemas along user-defined search paths, it cannot access these standard schemas from the backend package assets. These standard schemas can be loaded using the PublishedSchemaXmlFileLocater.

Constructor

The PublishedSchemaXmlFileLocater class takes a single argument: the native assets directory path of the backend package. This directory path can be accessed using the KnownLocations.nativeAssetsDir getter provided by the core-backend package.

Usage

The primary purpose of PublishedSchemaXmlFileLocater is to locate the standard schemas released by the core-backend package, making it a read-only locater. User-defined schemas should always take precedence over standard schemas. Therefore, when a schema context has multiple locaters, the PublishedSchemaXmlFileLocater should be added last to the locater list. This ensures that standard schemas are loaded only as a fallback when no user-defined version of the schema can be found.

The SchemaContext provides a method to achieve this: addFallbackLocater(locater: ISchemaLocater). This method ensures that the locater remains at the end of the list, regardless of any existing locaters in the context or any new locaters added subsequently. Calling addFallbackLocater with the PublishedSchemaXmlFileLocater ensures that standard schemas are considered as fallbacks.

Example

```typescript import { SchemaContext } from "@itwin/ecschema-metadata"; import { PublishedSchemaXmlFileLocater } from "@itwin/ecschema-locaters"; import { KnownLocations } from "@itwin/core-backend";

const schemaContext = new SchemaContext(); const publishedSchemaLocater = new PublishedSchemaXmlFileLocater(KnownLocations.nativeAssetsDir); schemaContext.addFallbackLocater(publishedSchemaLocater);