DL_DataGetFirst
» Table of Contents |  | | » Glossary | | | » Index | | |
| | |
| ||
| ||
SYNOPSIS
# include <cssm.h>
|
|
|
PARAMETERS
| DLDBHandle (input) | ||
The handle pair that describes the add-in data storage library module to be used to perform this function and the open data store to search for records satisfying the query. | ||
| Query (input/optional) | ||
The query structure specifying the selection predicate(s) used to query the data store. The structure contains meta information about the search fields and the relational and conjunctive operators forming the selection predicate. The comparison values to be used in the search are specified in the Attributes field of this Query structure. If a search attribute is of type CSSM_DB_ATTRIBUTE_FORMAT_STRING and the search value specified for that string includes a null-terminator, then the length count for that string should include the terminating character. (If null-terminators are used they should be used consistently, storing the terminator as part of the string in the data store, otherwise selection predicates will not locate expected matches.) The Query structure attributes also identify the particular attributes to be searched by this query. If no query is specified, the DL module can return the first record in the data store, performing sequential retrieval, or return an error. If no selection predicates are specified, the DL module can return the first record in the data store, performing sequential retrieval, or return an error (CSSM_DL_UNSUPPORTED_NUM_SELECTION_PREDS). When selection predicates are specified, the NumberOfValues of the Attribute of each selection predicate must be 1. If any selection predicate does not satisfy this requirement, the error CSSMERR_DL_INVALID_QUERY is returned. | ||
| ResultsHandle (output) | ||
This handle should be used to retrieve subsequent records that satisfied this query. | ||
| Attributes (optional-input/output) | ||
If the Attributes structure pointer is NULL, no values are returned. Otherwise, the DataRecordType, NumberOfAttributes and AttributeData fields are read. AttributeData must be an array of NumberOfAttributes CSSM_DB_RECORD_ATTRIBUTE elements. Only the Info field of each element is used on input. The AttributeFormat field of the Info field is ignored on input. On output, a CSSM_DB_RECORD_ATTRIBUTE structure containing a list of all or the requested attribute values (subset) from the retrieved record. The SemanticInformation field is set. For each CSSM_DB_ATTRIBUTE_DATA contained in the AttributeData array, the NumberOfValues field is set to reflect the size of the Value array which is allocated by the DL using the application specified allocators. Each CSSM_DATA in the Value array will have it's Data field as a pointer to data allocated using the application specified allocators containing the attributes value, and have it's Length set to the length of the value. All values for an attribute are returned (this could be 0). All fields in the Info field of the CSSM_DB_ATTRIBUTE_DATA are left unchanged except for the AttributeFormat field, which is set to reflect the schema. | ||
| Data (optional-input/output) | ||
Data values contained in the referenced memory are ignored during processing and are overwritten with the retrieved opaque object. On output, a CSSM_DATA structure containing the opaque object stored in the retrieved record. | ||
| UniqueId (output) | ||
If successful and (at least) a record satisfying the query has been found, then this parameter returns a pointer to a CSSM_UNIQUE_RECORD_PTR structure containing a unique identifier associated with the retrieved record. This unique identifier structure can be used in future references to this record using this DLDBHandle pairing. It may not be valid for other DLHandles targeted to this DL module or to other DBHandles targeted to this data store. If there are no records satisfying the query, then this pointer is NULL and CSSM_DL_DataGetFirst() must return CSSM_DL_ENDOFDATA; in this case a normal termination condition has occurred. The CSSM_DL_FreeUniqueRecord() must be used to deallocate this structure. | ||
DESCRIPTION
This function retrieves the first data record in the data store that matches the selection criteria. The selection criteria (including selection predicate and comparison values) is specified in the Query structure. If the Query specifies an attribute that is not defined in the database's meta-information, an error condition is returned. The DL module can use internally-managed indexing structures to enhance the performance of the retrieval operation. This function selects the first record satisfying the query based on the list of Attributes and the opaque Data object. The output buffers for the retrieved record are allocated by this function using the memory management functions provided during the module attach operation. This function also returns a results handle to be used when retrieving subsequent records satisfying the query.
Additional matching records are iteratively retrieved using the CSSM_DL_DataGetNext() function . The data storage module supports one of two retrieval models:
Transactional - all query results are determined at initial query evaluation. Results do not change during an incremental retrieval process.
File System Scan - query results are selected during the incremental retrieval process. Records matching the query may be added to or deleted from the underlying data store during the iterative retrieval. The caller may receive the new matching records and not received the deleted records.
The caller can determine which retrieval model is supported by examining the encapsulated product description for this data storage module.
If the query selection criteria also specifies time for space limits for executing the query, those limits also apply ro retrieval of the additional selected data records retrieved using the CSSM_DL_DataGetNext() function. Finally, this function returns a unique record identifier associated with the retrieved record. This structure can be used in future references to the retrieved data record. Once a user has finished using a certain query, it must call CSSM_DataAbortQuery() for releasing resources that CSSM uses. If all records satisfying the query have been retrieved, then query is automatically terminated.
RETURN VALUE
A CSSM_RETURN value indicating success or specifying a particular error condition. The value CSSM_OK indicates success. All other values represent an error condition.
ERRORS
Errors are described in the CDSA Technical Standard.
|
|
|