olapclient

A Windows DLL (and Python + R wrappers) for connecting to Microsoft Analysis Services OLAP cubes — both multidimensional (MDX) and tabular (DAX) models — via the MSOLAP OLE DB provider.

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Repository layout

olapclient.h          C API header (share with callers)
olapclient.cpp        DLL implementation
olapclient.vcxproj    Visual Studio 2022 DLL project
olapclient.sln        Solution file

python/
  olapclient/
    __init__.py       Python package (ctypes-based)
  setup.py

R/
  olapclientR/
    DESCRIPTION
    NAMESPACE
    R/olap.R          R package functions
    src/
      r_wrapper.cpp   R ↔ DLL glue (.Call API)
      Makevars.win    Windows build settings

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Prerequisites

Component	Where to get it
Windows 10/11 (64-bit)	—
Visual Studio 2019/2022 with C++ workload	visualstudio.microsoft.com
MSOLAP OLE DB provider	Installed with SQL Server, SSMS, or the standalone download
Python ≥ 3.7 (Python wrapper)	python.org
R ≥ 4.0 with Rtools (R wrapper)	r-project.org

Note on cross-platform use: The DLL itself relies on Windows COM/OLE DB and only runs on Windows. The Python and R packages are structured so they can be distributed cross-platform; on non-Windows systems they will raise a clear error directing users to XMLA/JDBC alternatives.

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Building the DLL

1. Open olapclient.sln in Visual Studio 2022.
2. Select Release | x64 (or the architecture that matches your Python/R install).
3. Build → the DLL lands in bin\x64\Release\olapclient.dll.

MSOLAP type library: The project imports ADO via its COM GUID (libid:00000205-0000-0010-8000-00AA006D2EA4), so no hard-coded path to msado15.dll is needed.

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Connection string formats

On-premises (multidimensional or tabular)

Provider=MSOLAP;Data Source=<server>\<instance>;Initial Catalog=<database>;

Azure Analysis Services

Provider=MSOLAP;Data Source=asazure://<region>.asazure.windows.net/<server>;
Initial Catalog=<database>;
User ID=<upn>;Password=<password>;Persist Security Info=True;

Power BI Premium (XMLA endpoint)

Provider=MSOLAP;Data Source=powerbi://api.powerbi.com/v1.0/myorg/<workspace>;
Initial Catalog=<dataset>;User ID=app:<app_id>@<tenant_id>;Password=<secret>;

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Python usage

from olapclient import OlapClient, QueryType

conn_str = "Provider=MSOLAP;Data Source=myserver;Initial Catalog=AdventureWorks;"

# --- MDX (multidimensional) ---
with OlapClient(conn_str) as client:
    result = client.execute_mdx("""
        SELECT
          NON EMPTY {[Measures].[Internet Sales Amount]} ON COLUMNS,
          NON EMPTY {[Date].[Calendar Year].Members}     ON ROWS
        FROM [Internet Sales]
    """)
    print(result.columns)
    print(result.rows[0])        # first row as list of strings
    df = result.to_df()          # pandas DataFrame (requires pandas)

# --- DAX (tabular) ---
with OlapClient(conn_str) as client:
    df = client.execute_dax(
        "EVALUATE SUMMARIZECOLUMNS('Date'[Calendar Year], "
        "\"Sales\", [Internet Sales Amount])"
    )

Installation

# 1. Build olapclient.dll (see above) and copy to python/olapclient/
cp bin/x64/Release/olapclient.dll python/olapclient/

# 2. Install the package
pip install ./python

# Optional pandas support
pip install "./python[pandas]"

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R usage

library(olapclientR)

conn_str <- "Provider=MSOLAP;Data Source=myserver;Initial Catalog=AdventureWorks;"
conn     <- olap_connect(conn_str)

# MDX – multidimensional cube
df_mdx <- olap_execute_mdx(conn, "
  SELECT
    NON EMPTY {[Measures].[Internet Sales Amount]} ON COLUMNS,
    NON EMPTY {[Date].[Calendar Year].Members}     ON ROWS
  FROM [Internet Sales]
")

# DAX – tabular model
df_dax <- olap_execute_dax(conn,
  "EVALUATE SUMMARIZECOLUMNS('Date'[Calendar Year], \"Sales\", [Internet Sales Amount])"
)

olap_disconnect(conn)

Installation

# 1. Set the path to the folder containing olapclient.h and olapclient.lib
Sys.setenv(OLAPCLIENT_DIR = "C:/path/to/olapclient/bin/x64/Release")

# 2. Install from source
install.packages("R/olapclientR", repos = NULL, type = "source")

Tip: The .lib import library is generated by MSVC alongside the DLL. Point OLAPCLIENT_DIR at the directory containing both olapclient.dll, olapclient.lib, and olapclient.h.

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API reference

C API (olapclient.h)

Function	Description
olap_connect(conn_str)	Open a connection; returns OLAP_CONN or NULL
olap_disconnect(conn)	Close and free the connection
olap_is_connected(conn)	Returns 1 if open
olap_execute(conn, query, type)	Run MDX/DAX; returns OLAP_RESULT or NULL
olap_free_result(result)	Release result memory
olap_get_column_count(result)	Number of columns
olap_get_row_count(result)	Number of rows
olap_get_column_name(result, col)	Column name string
olap_get_value(result, row, col)	Cell value as UTF-8 string
olap_get_last_error()	Last error message (thread-local)
olap_get_version()	DLL version string

query_type constants: OLAP_QUERY_MDX = 0, OLAP_QUERY_DAX = 1

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Notes

• MDX flattened results: ADO + MSOLAP returns MDX results as a flat two-dimensional recordset. Use NON EMPTY and axis ordering to control which dimensions appear as columns.
• DAX dialect: MSOLAP 11+ (SQL Server 2012+) auto-detects DAX vs MDX. Pass OLAP_QUERY_DAX as an explicit hint; the implementation also sets the dialect on the connection when supported.
• Thread safety: Each thread should call olap_connect separately; connections are not shared across threads. Error messages are stored thread-locally.
• NULL values: Empty cells and server-side NULLs are returned as an empty string "" in C/Python and as NA_character_ in R.