--- title: Expression Query source: https://vjmap.com/en/guide/exprQuery.html --- # Expression Query When CAD drawings are opened directly in `memory mode`, there is no process of converting to a `spatial database`, so the frontend cannot perform custom queries on backend data via `sql`. Queries can only be performed through `js scripts` or through `expressions`. For expression syntax details, see the document [Server-side Rendering Expression Syntax](/en/guide/expr.html). ::: tip Tip `js scripts` are easier to understand and get started with, but slightly slower in performance `Expressions` are harder to understand and master, but perform better We recommend using `js scripts` ::: ## Built-in Variables | Variable | Description | Type | Example | |:---|:---|:---|:---| |gInLayerIndex|Current entity layer index|(numeric)|0| |gInObjectId|Current entity object ID|(string)|'283' e.g. gInObjectId=='283' |gInFeatureType|Current entity type|(string)|'AcDbPolyline' e.g. gInFeatureType=='AcDbPolyline' |gInLayerName|Current entity layer name|(string)|'Layer1' e.g. gInLayerName=='Layer1' |gInColor|Current entity color|(numeric)|4278255615 |gInColorRed|Current entity color (red component)|(numeric)|255 |gInColorGreen|Current entity color (green component)|(numeric)|255 |gInColorBlue|Current entity color (blue component)|(numeric)|0 |gInColorAlpha|Current entity color (alpha component)|(numeric)|0 |println|Debug output function| |gInExtendMinX|Current entity extent (bottom-right X)|(numeric)|700.10 |gInExtendMinY|Current entity extent (bottom-right Y)|(numeric)|10.01 |gInExtendMaxX|Current entity extent (top-left X)|(numeric)|800.20 |gInExtendMaxY|Current entity extent (top-left Y)|(numeric)|20.02 |gInAttrs1|Current entity attribute 1 value|(string) s1 linetype| |gInAttrs2|Current entity attribute 2 value|(string) s2 extended dictionary data| |gInAttrs3|Current entity attribute 3 value|(string) s3 varies by entity type| |gInAttrs4|Current entity attribute 4 value|(string) s4 string attribute data, varies by entity type| |gInAttrs5|Current entity attribute 5 value|(string) s5 string attribute data, varies by entity type| |gInAttrn6|Current entity attribute 6 value|(numeric) n1 color index| |gInAttrn7|Current entity attribute 7 value|(numeric) n2 linetype scale| |gInAttrn8|Current entity attribute 8 value|(numeric) n3 line width| |gInAttrn9|Current entity attribute 9 value|(numeric) n4 transparency| |gInAttrn10|Current entity attribute 10 value|(numeric) n5 numeric attribute data, varies by entity type| |gInAttrn11|Current entity attribute 11 value|(numeric) n6 varies by entity type| |gInAttrn12|Current entity attribute 12 value|(numeric) n7 varies by entity type| |gInAttrn13|Current entity attribute 13 value|(numeric) n8 varies by entity type| |gInAttrn14|Current entity attribute 14 value|(numeric) n9 varies by entity type| |gInAttrn15|Current entity attribute 15 value|(numeric) n10 varies by entity type| |gInCoordX|Current entity X coordinate array|(numeric array)|[10,20...] gInCoordX[0]=10| |gInCoordY|Current entity Y coordinate array|(numeric array)|[10,20...] gInCoordY[0]=10| |gInCoordZ|Current entity Z coordinate array|(numeric array)|[10,20...] gInCoordZ[0]=10| |gInCoordCount|Current entity coordinate count|(numeric)|2| |gOutColorRed|Output color (red component) (modify current entity color)|(numeric)|255, e.g. gOutColorRed := 255; means all levels have red component 255; can also be array, e.g. gOutColorRed[0] := 122;gOutColorRed[5] := 200; means levels 1-4 have red 122, level 5+ has red 200 |gOutColorGreen|Output color (green component) (modify current entity color)|(numeric)|255, same usage as above |gOutColorBlue|Output color (blue component) (modify current entity color)|(numeric)|255, same usage as above |gOutColorAlpha|Output color (alpha component) (modify current entity color)|(numeric)|255, same usage as above |gOutLineWidth|Output line width (modify current entity line width)|(numeric)|3, same usage as above |gOutVisible|Output visibility (modify current entity visibility)|(numeric)|1 or 0, same usage as above |gOutReturn|0 do not add to selection set; 1 add to selection set| ## Supported CAD Entity Types | Class Name | Description | Type Value | |:---------------------------|:---|:----| | AcDbLine | Line | 1 | | AcDbPolyline | Polyline | 2 | | AcDb2dPolyline | 2D Polyline | 3 | | AcDb3dPolyline | 3D Polyline | 4 | | AcDbSpline | Spline | 5 | | AcDbArc | Arc | 6 | | AcDbCircle | Circle | 7 | | AcDbEllipse | Ellipse | 8 | | AcDbCurve | Curve | 9 | | AcDbBlockReference | Block Reference | 10 | | AcDbHatch | Hatch | 11 | | AcDbMText | Multiline Text | 12 | | AcDbText | Single-line Text | 13 | | AcDbShape | Shape | 14 | | AcDbRasterImage | Raster Image | 15 | | AcDbWipeout | Wipeout | 16 | | AcDb2LineAngularDimension | Angular Dimension [two lines] | 17 | | AcDb3PointAngularDimension | Angular Dimension [three points] | 18 | | AcDbAlignedDimension | Aligned Dimension | 19 | | AcDbArcDimension | Arc Dimension | 20 | | AcDbDiametricDimension | Diametric Dimension | 21 | | AcDbOrdinateDimension | Ordinate Dimension | 22 | | AcDbRadialDimension | Radial Dimension | 23 | | AcDbRadialDimensionLarge | Radial Dimension Large | 24 | | AcDbRotatedDimension | Rotated Dimension | 25 | | AcDbAttributeDefinition | Attribute Definition | 26 | | AcDbAttribute | Block Attribute | 27 | | AcDbTable | Table | 28 | | AcDbMLeader | MLeader | 29 | | AcDbRegion | Region | 30 | | AcDbPolyFaceMesh | Polyface Mesh | 31 | | AcDbPolygonMesh | Polygon Mesh | 32 | | AcDbSurface | Surface | 33 | | AcDb3dSolid | 3D Solid | 34 | | AcDbFace | 3D Face | 35 | | AcDbSolid | Solid | 36 | ## Expression Examples Query `all lines` in the drawing js ```js return gInFeatureType=='AcDbLine' ``` Query all `3D polylines` with `layer name "Layer1"` in the drawing ```js return (gInFeatureType=='AcDb3dPolyline' && gInLayerName=='Layer1') ``` Query `red` `single-line text` in the drawing ```js return (gInFeatureType=='AcDbText' && gInColorRed==255 && gInColorGreen==0 && gInColorBlue==0) ``` Query entity with `objectid` of `9BE` in the drawing ```js return gInObjectId=='9BE' ``` Query all text in the drawing (single-line text, multiline text, attribute definition, block attribute) ```js return (gInFeatureType=='AcDbText' || gInFeatureType=='AcDbMText' || gInFeatureType=='AcDbAttributeDefinition' || gInFeatureType=='AcDbAttribute') ``` Query all block entities in the drawing ```js return gInFeatureType=='AcDbBlockReference' ``` Query `lines with length 10` in the drawing ```js return (gInFeatureType=='AcDbLine' && gInAttrn11 == 10) ``` Query `circles with radius 5` in the drawing ```js return (gInFeatureType=='AcDbCircle' && gInAttrn12 == 5) ``` Query all `polylines` in the drawing with `layer "grid lines"` and `coordinate x greater than 10` ```js return (gInFeatureType == 'AcDbPolyline' && gInLayerName == 'grid lines' && gInExtendMinX >= 10) ``` ## Query Method ```ts /** * Expression query for entities * @param param Parameters * @param cb Callback for processing each point in the result. If null is returned, the default handler is used */ exprQueryFeature(param: IExprQueryFeatures, cb?: (point: [number, number]) => [number, number] | null | undefined): Promise; /** * Expression query entity parameters */ export interface IExprQueryFeatures extends IQueryBaseFeatures { /** Expression. */ expr: string; /** Record start position. */ beginpos?: number; } ``` When writing expressions, you need to return based on condition evaluation. Format: ```js return true; // or return false; ``` For example, to query all block entities in the drawing, the expression is: ```js return gInFeatureType == 'AcDbBlockReference' ``` Query usage: ```js let query = await svc.exprQueryFeature({ // Expression syntax // expr: `gOutReturn := if((gInFeatureType == 'AcDbPolyline' and gInLayerName == 'grid lines' and gInExtendMinX >= ${center.x} ), 1, 0);`, // Now also supports js syntax // expr: `if (gInFeatureType == 'AcDbPolyline' && gInLayerName == 'grid lines' && gInExtendMinX >= ${center.x} ) { // return true; // } else { // return false; // }`, // Filter all block entities (expression syntax) // expr: `gOutReturn := if((gInFeatureType == 'AcDbBlockReference'), 1, 0);`, // Filter all block entities (js syntax) expr: `return gInFeatureType == 'AcDbBlockReference'`, fields: "objectid,blockname,envelop", useCache: true, limit: 1000000 // Large value, equivalent to finding all }) ``` 
// --Backend query entity data [memory rendering]--Query entity data by conditions in the backend when opening uploaded CAD DWG files directly in memory mode
let svc = new vjmap.Service(env.serviceUrl, env.accessToken)
let res = await svc.openMap({
    mapid: env.exampleMapId,
    mapopenway: vjmap.MapOpenWay.Memory, // Open in memory rendering mode
    style: vjmap.openMapDarkStyle()
})
if (res.error) {
    message.error(res.error)
}
let mapExtent = vjmap.GeoBounds.fromString(res.bounds);
let prj = new vjmap.GeoProjection(mapExtent);
let center = mapExtent.center();
let map = new vjmap.Map({
    container: 'map', // container ID
    style: svc.rasterStyle(),
    center: prj.toLngLat(center),
    zoom: 2,
    renderWorldCopies: false
});
map.attach(svc, prj);
map.fitMapBounds();
map.addControl(new vjmap.NavigationControl());
map.addControl(new vjmap.MousePositionControl({showZoom: true}));
const handleQuery= async () => {
    let query = await svc.exprQueryFeature({
        // Filter all block entities
        expr: `return gInFeatureType == 'AcDbBlockReference'`,
        fields: "objectid,blockname,envelop",
        useCache: true,
        limit: 1000000 // Large value, equivalent to finding all
    })
    if (query.error) {
        message.error(query.error)
    } else {
        // Filter results by block name
        let polygons = []
        for(let i = 0; i < query.result.length; i++) {
            let blockname = query.result[i].blockname;
            let bounds = map.getEnvelopBounds(query.result[i].envelop);
            polygons.push({
                points: map.toLngLat(bounds.toPointArray()),
                properties: {
                    name: "objectid:" + query.result[i].objectid,
                    color: '#ff00ff'
                }
            });
        }
        map.logInfo(`Query result count: ${query.recordCount}`)
        // Draw the found blocks
        let polygon = new vjmap.Polygon({
            data: polygons,
            fillColor: ['case', ['to-boolean', ['feature-state', 'hover']], 'yellow', ['get', 'color']],
            fillOpacity: ['case', ['to-boolean', ['feature-state', 'hover']], 0.8, 0.5],
            // If you don't want to show the polygon initially, set opacity to 0, it will show on hover
            // fillOpacity: ['case', ['to-boolean', ['feature-state', 'hover']], 0.8, 0.0],
            fillOutlineColor: ['get', 'color'],
            isHoverPointer: true,
            isHoverFeatureState: true
        });
        polygon.addTo(map);
    }
};
handleQuery()


## Combining Expression Query and SQL Query [View online demo: Multiple queries for maximum sub-entity area of block objects](https://vjmap.com/demo/#/demo/map/service/22findzmultiquery) ```js // --Multiple queries for maximum sub-entity area of block objects--Query the entity with the largest area in blocks, first via expression query, then via condition query. Analyze results together let svc = new vjmap.Service(env.serviceUrl, env.accessToken) let res = await svc.openMap({ mapid: env.exampleMapId, mapopenway: vjmap.MapOpenWay.GeomRender, // Open in geometry rendering mode style: vjmap.openMapDarkStyle() }) if (res.error) { message.error(res.error) } let mapExtent = vjmap.GeoBounds.fromString(res.bounds); let prj = new vjmap.GeoProjection(mapExtent); let center = mapExtent.center(); let map = new vjmap.Map({ container: 'map', // container ID style: svc.rasterStyle(), center: prj.toLngLat(center), zoom: 2, renderWorldCopies: false }); map.attach(svc, prj); map.fitMapBounds(); map.addControl(new vjmap.NavigationControl()); map.addControl(new vjmap.MousePositionControl({showZoom: true})); // let blockNames = ["M_F13", "_AXISO"]; // Block name list to find. Block names can be found in the cloud management platform by clicking a block entity and checking blockname in the right-side properties const handleQuery= async () => { let query = await svc.exprQueryFeature({ expr: `return gInFeatureType == 'AcDbBlockReference'`, fields: "objectid,blockname,layername,positon,rotate,scaleX,scaleY,scaleZ", // Empty means all fields geom: false, // Memory mode useCache: true, limit: 1000000 // Large value, equivalent to finding all }) if (query.error) { message.error(query.error) return } // Filter results by block name // let findBlockName = new Set(blockNames); let objectIds = new Set(); // Block object objectid values let blockEntities = []; for(let i = 0; i < query.result.length; i++) { let blockname = query.result[i].blockname; // if (!findBlockName.has(blockname)) { // If not in the target list // continue // } blockEntities.push(query.result[i]) objectIds.add(query.result[i].objectid) } // Below, condition query for specific sub-entities contained in all blocks by objectid. This data cannot be obtained via memory query. Only after geometry processing decomposes blocks into individual sub-entities can condition query be used // In condition query, sub-entities of the same block all have objectid prefixed with that block's objectid_ // Entity id // Block objectid naming rule: block_id_referenced_block_def_id1_referenced_block_def_id2(may have multiple)_entity_id_#; // Table naming rule: objectid naming rule: block_id_referenced_block_def_id1_referenced_block_def_id2(may have multiple)_entity_id_@; // Group objectid naming rule: $entity_id_element_index_in_entity$group_id; // Build sql condition, query all block objectid_ prefixed at once for efficiency // For fuzzy search, % can be used as wildcard in like. % defines wildcards before/after the pattern. like 'k%' finds strings ending with 'k' let condtionIds = Array.from(objectIds).map(id => `objectid like '${id}_%' `).join(" or ") // Concatenate all matching ids let condQuery = await svc.conditionQueryFeature({ condition: condtionIds, // objectid matching the above condition fields: "objectid,area", geom: true, limit: 100000 // Set large, equivalent to getting all. Default 100 if not specified }) if (query.error) { message.error(query.error) return } let blockFeatures = [] for(let i = 0; i < condQuery.result.length; i++) { let item = condQuery.result[i]; blockFeatures.push(item) } // Find related entities under all blocks, find the sub-entity with maximum area let showDatas = [] for(let block of blockEntities) { // All starting with block objectid_ are sub-entities of that block let blockFeature = blockFeatures.filter(b => b.objectid.indexOf(block.objectid + "_") === 0) let maxArea = Math.max(...blockFeature.filter(b => b.area).map(d => d.area)) showDatas.push({ ...block, area: maxArea }) } console.table(showDatas) message.info(`Query result count: ${blockEntities.length} Press F12 to view console for details`); }; handleQuery(); ```