// URL format of the POST query to read data from DataService.
http(s)://[Bpm'online application address]/[Configuration number]/dataservice/[Data fromat]/reply/SelectQuery
// URL example of the POST query to read data from DataService.
http(s)://example.bpmonline.com/0/dataservice/json/reply/SelectQuery

{
    "RootSchemaName":"[Object root schema name]",
    "OperationType":[Type of record operation],
    "Columns":{
        "Items":{
            "Name":{
                "OrderDirection":[Sorting order],
                "OrderPosition":[Column position],
                "Caption":"[Title]",
                "Expression":{
                    "ExpressionType":[Expression type],
                    "ColumnPath":"[Path to column]",
                    "Parameter":[Parameter],
                    "FunctionType":[Function type],
                    "MacrosType":[Macro type],
                    "FunctionArgument":[Function argument],
                    "DatePartType":[Type of date part],
                    "AggregationType":[Aggregation type],
                    "AggregationEvalType":[Aggregation scope],
                    "SubFilters":[Buit-in filters]
                }
            }
        }
    },
    "AllColumns":[Indicates that all columns are selected],
    "ServerESQCacheParameters":{
        "CacheLevel":[Caching level],
        "CacheGroup":[Caching group],
        "CacheItemName":[Record key in repository]
    },
    "IsPageable":[Indicates page-by-page],
    "IsDistinct":[Indicates uniqueness],
    "RowCount":[Number of selected records],
    "ConditionalValues":[Conditions for building a pageable query],
    "IsHierarchical":[Indicates hierarchical data selection],
    "HierarchicalMaxDepth":[Maximum nesting level of the hierarchical query],
    "HierarchicalColumnName":[Column name used to create hierarchical query],
    "HierarchicalColumnValue":[Initial value of hierarchical column],
    "Filters":[Filters]
    }
}

using System;
using System.Text;
using System.IO;
using System.Net;
using System.Collections.Generic;
using Terrasoft.Nui.ServiceModel.DataContract;
using Terrasoft.Core.Entities;
using System.Web.Script.Serialization;
using Terrasoft.Common;

// Bpm'online primary application URL. Must be replaced with a custom one.
private const string baseUri = @"http://example.bpmonline.com";
// Query string to the Login method of the AuthService.svc service.
private const string authServiceUri = baseUri + @"/ServiceModel/AuthService.svc/Login";
// SelectQuery path string.
private const string selectQueryUri = baseUri + @"/0/DataService/json/SyncReply/SelectQuery";
// Bpm'online authentication cookie.
private static CookieContainer AuthCookie = new CookieContainer();

// Instance of the query class.
var selectQuery = new SelectQuery()
{
    // Root schema name.
    RootSchemaName = "Contact",
    // Collection of query columns.
    Columns = new SelectQueryColumns()
};
// Expression that specifies the type of [[Full name] column.
var columnExpressionName = new ColumnExpression()
{
    // Expression type — schema column.
    ExpressionType = EntitySchemaQueryExpressionType.SchemaColumn,
    // Path to column.
    ColumnPath = "Name"
};
// Configuring the [Name] column. 
var selectQueryColumnName = new SelectQueryColumn()
{
    //Title.
    Caption = "Full name",
    // Sorting order — ascending.
    OrderDirection = OrderDirection.Ascending,
    // Sorting order position.
    OrderPosition = 0,
    // Expression that specifies column type.
    Expression = columnExpressionName
};
// Expression that specifies [Number of activities] column type.
var columnExpressionActivitiesCount = new ColumnExpression()
{
    // Expression type — subquery.
    ExpressionType = EntitySchemaQueryExpressionType.SubQuery,
    // Path to column in relation to root schema.
    ColumnPath = "[Activity:Contact].Id",
    // Function type — aggregation.
    FunctionType = FunctionType.Aggregation,
    // Aggregation type — quantity.
    AggregationType = AggregationType.Count
};
// Configuring the [Number of activities] column.
var selectQueryColumnActivitiesCount = new SelectQueryColumn()
{
    //Title.
    Caption = "Number of activities",
    // Sorting direction — ascending.
    OrderDirection = OrderDirection.Ascending,
    // Sorting order position.
    OrderPosition = 1,
    // Expression, which specifies column type.
    Expression = columnExpressionActivitiesCount
};

// Adding columns to query.
selectQuery.Columns.Items = new Dictionary<string, SelectQueryColumn>()
{
    {
        "Name",
        selectQueryColumnName
    },
    {
        "ActivitiesCount",
        selectQueryColumnActivitiesCount
    }
};
// Serialization of an instance of query class to add to JSON string.
var json = new JavaScriptSerializer().Serialize(selectQuery);

// Converting a JSON object string to a byte array.
byte[] jsonArray = Encoding.UTF8.GetBytes(json);
// Creating an instance of HTTP request.
var selectRequest = HttpWebRequest.Create(selectQueryUri) as HttpWebRequest;
// Defining request method.
selectRequest.Method = "POST";
// Defining request content type.
selectRequest.ContentType = "application/json";
// Adding earlier received authentication cookies to a data fetch query.
selectRequest.CookieContainer = AuthCookie;
// Set length for request content.
selectRequest.ContentLength = jsonArray.Length;
// Placing JSON object to request content.
using (var requestStream = selectRequest.GetRequestStream())
{
    requestStream.Write(jsonArray, 0, jsonArray.Length);
}
// Executing HTTP request and getting reply from server.
using (var response = (HttpWebResponse)selectRequest.GetResponse())
{
    // Displaying reply in console.
    using (StreamReader reader = new StreamReader(response.GetResponseStream()))
    {
        Console.WriteLine(reader.ReadToEnd());
    }
}

//Setup of section button display.
diff: /**SCHEMA_DIFF*/[
    // Metadata for adding a custom button in a section.
    {
        // Indicates that an elementis added on a page.
        "operation": "insert",
        // Meta name of the parent control element where the button is added.
        "parentName": "ActionButtonsContainer",
        // Indicates that the button is added to the control element collection
        // of parent element (meta-name specified in parentName).
        "propertyName": "items",
        // Meta-name of the added button.
        "name": "SelectQueryContactButton",
        // Additional properties of the element.
        "values": {
            // Type of added element - button.
            itemType: Terrasoft.ViewItemType.BUTTON,
            // Binding button title to a schema localizable string.
            caption: { bindTo: "Resources.Strings.SelectQueryContactButtonCaption" },
            // Binding of the button pressing handler method.
            click: { bindTo: "onSelectQueryContactClick" },
            "layout": {
                "column": 1,
                "row": 6,
                "colSpan": 1
            }
        }
    }

]/**SCHEMA_DIFF*/

methods: {
    // Handler method for button click.
    onSelectQueryContactClick: function() {
        // Creating an instance of the Terrasoft.InsertQuery class.
        var select = Ext.create("Terrasoft.EntitySchemaQuery", {
            // Root schema name.
            rootSchemaName: "Contact"
        });
        // Adding the [Full name] column to query.
        select.addColumn("Name");
        // Adding [Number of activities] aggregate column to a query.
        select.addAggregationSchemaColumn(
            // Path to column in relation to the root schema.
            "[Activity:Contact].Id",
            // Aggregation type — quantity.
            Terrasoft.AggregationType.COUNT,
            // Column title.
            "ActivitiesCount",
            // Aggregation function scope - for all elements.
            Terrasoft.AggregationEvalType.ALL);
        // Update query to server
        // Getting whole collection of records and displaying it in the browser console.
        select.getEntityCollection(function(result) {
            if (!result.success) {
                // Processing/logging of error.
                this.showInformationDialog("Data query error");
                return;
            }
            // Displayed message.
            var message = "";
            // Analyzing resulting collection and generating displayed message.
            result.collection.each(function(item) {
                message += "Full name: " + item.get("Name") +
                ". Number of activities: " + item.get("ActivitiesCount") + "\n";
            });
            // Displaying message in console.
            window.console.log(message);
        }, this);
    }
}