[offline] Document the database schema
This commit is contained in:
Thiago Marcos P. Santos
@@ -1,55 +1,159 @@
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CREATE TABLE resources ( -- Generic table for style, source, sprite, and glyph resources.
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id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
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url TEXT NOT NULL,
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kind INTEGER NOT NULL,
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expires INTEGER,
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modified INTEGER,
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etag TEXT,
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data BLOB,
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compressed INTEGER NOT NULL DEFAULT 0,
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accessed INTEGER NOT NULL,
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must_revalidate INTEGER NOT NULL DEFAULT 0,
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--
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-- Table containing the style, source, sprite, and glyph
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-- resources. Essentially everything that is not a tile.
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--
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CREATE TABLE resources (
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id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, -- Primary key.
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url TEXT NOT NULL, -- The URL of the resource without the access token. If a Mapbox
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-- resource, will be stored using the mapbox:// schema. Must be
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-- unique and that is enforced by the database schema.
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kind INTEGER NOT NULL, -- Type of the resource, taken from Resource::Kind enumeration:
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-- style = 1
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-- source = 2
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-- tile = 3
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-- glyphs = 4
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-- sprite image = 5
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-- sprite JSON = 6
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-- image = 7
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expires INTEGER, -- Expiration time. The resource will be refreshed after this
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-- expiration is reached.
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modified INTEGER, -- Last time the resource was modified.
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etag TEXT, -- Checksum used for cache optimization. If, when refreshing the
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-- resource, it matches the etag on the server, the resource will
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-- not get re-downloaded. See:
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-- https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/ETag
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data BLOB, -- Contents of the resource.
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compressed INTEGER NOT NULL DEFAULT 0, -- If the resource is compressed with Deflate or not. Compression is
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-- optional and should be used when the compression ratio is
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-- significant. Using compression will make decoding time slower
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-- because it will add an extra decompression step.
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accessed INTEGER NOT NULL, -- Last time the resource was used by GL Native. Useful for when
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-- evicting the least used resources from the cache.
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must_revalidate INTEGER NOT NULL DEFAULT 0, -- When set to true, the resource will not be used unless it gets
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-- first revalidated by the server.
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UNIQUE (url)
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);
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--
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-- Table containing all tiles, both vector and raster.
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--
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CREATE TABLE tiles (
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id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
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url_template TEXT NOT NULL,
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pixel_ratio INTEGER NOT NULL,
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z INTEGER NOT NULL,
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x INTEGER NOT NULL,
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y INTEGER NOT NULL,
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expires INTEGER,
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modified INTEGER,
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etag TEXT,
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data BLOB,
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compressed INTEGER NOT NULL DEFAULT 0,
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accessed INTEGER NOT NULL,
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must_revalidate INTEGER NOT NULL DEFAULT 0,
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id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, -- Primary key.
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url_template TEXT NOT NULL, -- The URL of the resource without the access token and without
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-- the tiles id substituted. Mapbox tiles will be stored using
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-- the mapbox:// schema. Example:
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-- mapbox://tiles/user.dataset/{z}/{x}/{y}.vector.pbf
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pixel_ratio INTEGER NOT NULL, -- The tile pixel ratio, typically 1 for vector tiles.
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z INTEGER NOT NULL, -- The zoom level of the tile.
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x INTEGER NOT NULL, -- The x position of the tile on the tile grid.
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y INTEGER NOT NULL, -- The y position of the tile on the tile grid.
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expires INTEGER, -- Expiration time. The tile will be refreshed after this
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-- expiration is reached. Expired tiles can still be rendered,
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-- unless must_revalidate is set to true. If an expired tile
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-- gets rendered, it will be replaced by a newer version as soon
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-- as the network request with a new tile arrives.
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modified INTEGER, -- Last time the tile was modified.
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etag TEXT, -- Checksum used for cache optimization. If, when refreshing the
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-- tile, it matches the etag on the server, the tile will not
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-- get re-downloaded. See:
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-- https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/ETag
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data BLOB, -- Contents of the tile.
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compressed INTEGER NOT NULL DEFAULT 0, -- If the tile is compressed with Deflate or not. Compression is
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-- optional and should be used when the compression ratio is
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-- significant. Using compression will make decoding time slower
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-- because it will add an extra decompression step.
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accessed INTEGER NOT NULL, -- Last time the tile was used by GL Native. Useful for when
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-- evicting the least used tiles from the cache.
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must_revalidate INTEGER NOT NULL DEFAULT 0, -- When set to true, the tile will not be used unless it gets
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-- first revalidated by the server.
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UNIQUE (url_template, pixel_ratio, z, x, y)
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);
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--
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-- Regions define the offline regions, which could be a GeoJSON geometry,
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-- or a bounding box like this example:
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--
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-- {
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-- "bounds": [
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-- 37.2,
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-- -122.8,
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-- 38.1,
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-- -121.7
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-- ],
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-- "include_ideographs": false,
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-- "max_zoom": 15.0,
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-- "min_zoom": 0.0,
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-- "pixel_ratio": 1.0,
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-- "style_url": "mapbox://styles/mapbox/streets-v11"
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-- }
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--
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-- The semantic definition of the region is up to the user and
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-- it could be a city, a country or an arbitrary bounding box.
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--
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-- Regions can overlap, which will cause them to share resources
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-- when it is the case.
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--
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-- "include_ideographs" is set to true when CJK characters are
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-- include on the offline package. By default, CJK is rendered
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-- by GL Native client side using local fonts. Downloading CJK
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-- will increase the size of the database considerably.
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--
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CREATE TABLE regions (
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id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
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definition TEXT NOT NULL, -- JSON formatted definition of region. Regions may be of variant types:
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-- e.g. bbox and zoom range, route path, flyTo parameters, etc. Note that
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-- the set of tiles required for a region may span multiple sources.
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description BLOB -- User provided data in user-defined format
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id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, -- Primary key.
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definition TEXT NOT NULL, -- JSON formatted definition of a region, a bounding box
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-- or a GeoJSON geometry. See https://geojson.org.
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description BLOB -- User provided data in user-defined format.
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);
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--
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-- Table mapping resources to regions. A resource
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-- might be part of many regions. Resources without
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-- regions are part of the ambient cache.
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--
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CREATE TABLE region_resources (
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region_id INTEGER NOT NULL REFERENCES regions(id) ON DELETE CASCADE,
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resource_id INTEGER NOT NULL REFERENCES resources(id),
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UNIQUE (region_id, resource_id)
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);
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--
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-- Table mapping tiles to regions. A tile might
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-- be part of many regions, meaning that regions might
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-- overlap efficiently. Tiles without regions are part
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-- of the ambient cache.
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--
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CREATE TABLE region_tiles (
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region_id INTEGER NOT NULL REFERENCES regions(id) ON DELETE CASCADE,
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tile_id INTEGER NOT NULL REFERENCES tiles(id),
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UNIQUE (region_id, tile_id)
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);
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-- Indexes for efficient eviction queries
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--
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-- Indexes for efficient eviction queries.
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--
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CREATE INDEX resources_accessed
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ON resources (accessed);
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